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# Software engineer backend Interview Questions

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### Software Engineer at Apple was asked...

Jun 19, 2012
 You have a 100 coins laying flat on a table, each with a head side and a tail side. 10 of them are heads up, 90 are tails up. You can't feel, see or in any other way find out which side is up. Split the coins into two piles such that there are the same number of heads in each pile.36 AnswersAnswer #1: Place 50 coins into two piles on its edges so that both have the same amount of heads in each pile, neither facing up or down. Answer #2: Trick question, place 50 coins in both piles and in theory they all have heads just not necessarily facing up or down.agree with 2nd ansSplit into two piles, one with 90 coins and the other with 10. Flip over every coin in the pile with 10 coins.Show More ResponsesJust split into two piles, each with 50 coins. The question only asks 50 heads in each one, it doesn't ask for the number of heads up!!!Pick 10 coins from the pile, flip it and put it in the other pile. This will ensure that the number of heads up are equal in both the pilesPick 10 coins from the original 100 and put them in a separate pile. Then flip those 10 coins over. The two piles are now guaranteed to have the same number of heads. For a general solution of N heads and a total of M coins: 1.) Pick any N coins out of the original group and form a second pile. 2.) Flip the new pile of N coins over. Done. Example (N=2, M=6): Original group is HHTTTT (mixed randomly). Pick any two of these and flip them over. There are only three possible scenarios: 1: The two coins you picked are both tails. New groups are {HHTT} {TT} and when you flip the 2nd group you have {HHTT} and {HH}. 2.) The two coins you picked consist of one head and one tail. New groups are {HTTT} and {HT} and when you flip the 2nd group you have {HTTT} and {TH}. 3.) The two coins you picked are both heads. New groups are {TTTT} and {HH} and when you flip the 2nd group you have {TTTT} and {TT}.The question says "'You' can't feel, see or in any other way find out which side is up....' Can a team member? Cooperate with a fellow engineer, or other colleague, who can see the coins to solve the problem?Question has its answer in it... 10 coins are head up..... 90 coins are tail down..... so it means all 90 coins are head up.... Now, all you have to do is to split it into half. 50/50Let's generalise the question to where there are n heads and any number of tails on the table. Select any n coins. This set will contain m heads, where m is between 0 and n inclusive, and n - m tails. The other n - m heads will be in the remaining coins. We now have two piles: the selection of n coins with n-m tails and the remainder with n-m heads. All we have to do is flip the selection so that the n-m tails become n-m heads, the same number as the heads in the remainder. This is a straightforward extension of the 'pick any 10 coins and flip' answer correctly given above by several people.All of you are over thinking it. Read the last bloody line, "Split the coins into two piles such that there are the same number of heads in each pile" They're not asking for the heads to be up or down, just an equal amount & every coin has a head side so dividing the pile equally achieves that.100 coins total, 10 of them are heads up, 90 are tails up. Meaning all of them are heads up AND tails down. Split it 50/50 and you are done.It is not as easy as to just split it. And it says heads UP tails UP. Given 10 h, 90 t. Pick some random 10 coins call it P1. Rest is P2. In P1, (10-x) heads, (x) tails In P2, (x) heads, (90-x) tails Flip the coins in P1. In P1, (x) heads and (10-x) tails P1 and P2 have the same number of heads.reading these answers is such a confidence builder.Show More ResponsesI agree to trev, don't think anyone read the question.we already have 2 piles --> 90 coins with tails up and 10 coins with heads up, just flip over 10 of the coins from 90 coins that have tails up, we will have same number of coins with heads up in each pile.get all coins in your hands, shake them, drop them. for each coin there is a 50% probability to lay heads up, and 50% probability for tails down. now split i halfquestion doesn't need to look faces of which side is up after splitting it in two piles. split all coins in two part of 50 50 and they all have heads ...and thats what questioner asking..!and move them to the 10-coin pile.Take 40coins from 90-coin pile, flip them over and move to the 10-coin pile.It's really depends on whether Apple is hiring Software Engineers who are collaborators, mathematicians or tricksters. It's clear that Apple does hire Engineers who listen to the question accurately.Make two groups at random for 10 and 90 coins. Example:- G1(10) G2(90) case 1:- 6H,4T 4H,86T case2:- 3H,7T 7H,83T Now flip all coins of smaller group G1(10). The result will always have same Heads in each pile. G1(10) G2(90) case 1:- 6T,4H 4H,86T case2:- 3T,7H 7H,83TWe just get 5 coins head up put in each piles ==> we get the same number of head up in each pile. They just ask we "Split the coins into two piles such that there are the same number of heads in each pile" . They didn't say that we don't kow what is coin head up and they mixed together."The question says "'You' can't feel, see or in any other way find out which side is up....' Can a team member? Cooperate with a fellow engineer, or other colleague, who can see the coins to solve the problem?" This is the best answer yet! Completely out of the box answer and yet so simple.Show More ResponsesFlip every other coin, 90 Tails will get split into 45 Heads and 45 Tails. Similarly 10 Heads will get converted to 5 Head and 5 Tails, so now we have 50 heads (45 + 5) and 50 tails (45 + 5). Then just split them into two equal groups.AnswerMake a pile of 10 and flip them over. Then the number of heads is equal in both piles.question says both group should have equal heads, but doesnt specifiy, it should be up, hence, just grouping 50 each would solve the problemThis is a screw you question, but yeah if you take out 10 coins you can have anywhere between 0-10 heads for every head you have you have one less head in the other pile and one less tail in your pile of 10 coins. So if you have 100 coins 10 heads and you take lets say 10 coins 0 heads, 10 tails. The 90 coins has 10 heads. 1 heads, 9 tails. The 90 coins has 9 heads (you stole one when selecting 10 coins). 2 heads, 8 tails. The 90 coins has 8 heads (same you stole 2 when selecting 10 coins ect). 3 heads, 7 tails. The 90 coins has 7 heads. 4 heads, 6 tails. the 90 coins has 6 heads. 5 heads, 5 tails, the 90 coins has 5 heads. 6 heads, 4 tails, the 90 coins has 4 heads. 7 heads, 3 tails, the 90 coins has 3 heads. 8 heads, 2 tails, the 90 coins has 2 heads. 9 heads, 1 tails, the 90 coins has 1 heads. 10 heads, 0 tails, the 90 coins has 0 heads. As you can see whenever you take out 10 because your not only stealing from the pile of 90's heads your also offsetting the pile of 10 coins tails by 1 equally you have an equal connection between the tails you have in the pile of 10 coins as you do heads in the pile of 90 coins that your tails in 10 coins pile always equals heads in 90 coin pile. So you just flip over each coin in the pile of 10 coins and your tails becomes heads. So if you selected 1 head and in the 10 coins pile you had 9 heads in the 90 coins pile and 9 tails in the 10 coins pile, you are guaranteed after flipping each over once to have 9 heads in the 10 coins pile as tails becomes heads and 9 heads in the 90 coin pile, and ect, ect. This stands true for any pile that you know the amount of one category and 2 options, If you know you have 25 of one things, despite how many things there are if each thing had only two options like heads or tails, you know selecting 25 of them the same amount you know of one thing that when taking out 25 or the equal number of what you know of one thing is in there that what you unsucessfully try to filter out is the inverse of what you selected successfully to take out.Pick 10 coins, flip them and form a separate pile. The no.of tails in both pile will be equal inspite of your choice being a tails up coins or a heads up coins. Coz when u pick a tails up coin u r reducing the no.of tails up in the first pile and since u flip it its gonna b a heads up coin the second pile, if u r picking up a heads up a coin u turn it into a tails up coin in the second pile so that it can cancel out one tails up coin in the existing first pile.If it means heads up then separate the coins into one pile of 90 one pile of 10 then flip the ten coins it works with all scenarios Of sides you ended up choosing also like to point out that we can't feel them so we probably can't use our hands to flip them but I assume they would allow us to use something as how else would we separate themThe answer lies in the exact wording of the question "Split the coins into two piles such that there are the same number of heads in each pile. " It does not specify heads need to be face up, so you would simply split the piles in 50 each and you have the same number of coins with heads in each pile.Take ten coins (consider as one pile, Pile A and other 90 coins as another pile, Pile B). Now you have two piles. Turn all coins as in pile A, you will end up with same number of heads in both piles. Ex: Scenario 1: Consider in Pile A, there are 2 heads and 8 tails. Hence in Pile B there will 8 heads.Now when you turn all the coins in Pile A you will end with 8 heads in Pile A. Hence both Pile A and Pile B have same number of heads. Scenario 2: Consider in Pile A, there are 10 heads. Hence in Pile B there will be 0 heads.Now when you turn all the coins in Pile A, you will end with 0 heads in Pile A. Hence both Pile A and Pile B have same number of heads. Scenario 3: Consider in Pile A, there are 0 heads. Hence in Pile B there will be 10 heads.Now when you turn all the coins in Pile A, you will end with 10 heads in Pile A. Hence both Pile A and Pile B have same number of heads.Show More ResponsesTake 10 coins.Split into two piles of 5 each.Flip all coins in one pile.Both piles now have equal heads and tails.Take another 10 and go through the same procedure.Follow the same process for the entire original pile.You end up with two sets of 5 piles having equal no. of heads and tails.Combine all 5 piles on each side and it's done.Its very simple. step 1 take group of 10 coins from all now flip this pile and you will get your answer. how? lets see cases 100 total ( 10 H + 90T) so you get group of 10 from them so lets assume you will get 4 h+6T , and (6H + 84T) then flip this smaller one new group will be 4T+ 6H so now we 2 groups 1 new 1 old 4t+6h and 6h+85T both have same number of heads ....LITERAL ANGLE Split 50/50. Both piles have the same number of heads. Parameters do not require each pile to have the same number of heads facing upward. TEAMWORK ANGLE Ask the most efficient, skilled coin identification analyst at Apple to identify the coins so the skilled sorting robot can separate the piles equally. PATRONIZING ANGLE Take a picture of the table with your iPhone and sending to a laborer hired to come sort for you via a services app in the app store. NEXT LEVEL QUANTUM ANGLE If the coins are in no way observable, the question is impossible to answer because the coins are sitting next to Schrodinger's cat and thus are in a state of both heads and tails until observed. One or more comments have been removed. Please see our Community Guidelines or Terms of Service for more information.

### Financial Software Developer at Bloomberg L.P. was asked...

Oct 1, 2010
 An array of 99 elements contains integers from 1 to 100 with one missing element. Find the missing element.128 Answers1001. calculate the sum of elements in array say SUM 2. sum of numbers 1 to 100 is(n* (n+1))/2 = 5050 when n==100 3. missing element is (5050-SUM)100Show More ResponsesThe parameters of the question do not allow you to determine what element is missing. Either more information should be supplied, or all answers are equally correct.How could an array size of 99 elements contain 1 - 100? Should either be integers 1-99 or 2-100 , in either case there is no missing element. All indices are accounted for.Sum them and then subtract them from 5050. In general, if an array of size n - 1 elements has unique elements from 1 to n, then the missing element can be found by subtracting the sum of the elements in the array from sum(1 ... n) = n * (n + 1) / 2. Alternately, one could use a boolean array of length n with all values set to false and then for each value, set array[val - 1] to true. To find the missing value, scan through the array and find the index which is set to false. Return index + 1. This requires O(n) memory and two passes over an O(n) array (instead of constant memory and one pass), but has the advantage of actually allowing you to verify whether or not the input was well formed.Admittedly, this question is poorly posed; however, the answer they are looking for refers to the syntax/nomenclature of some (not all) programming languages to index arrays starting at “0.” As such the 1-100 stored values would be in entries 0-99 of the array.Read the question. Here are the steps to solve it: 1) find the sum of integers 1 to 100 2) subtract the sum of the 99 members of your set 3) the result is your missing element! Very satisfying!Sort array. While loop with an index variable with condition of next element being 1 greater than previous element. When loop breaks, return the value of the index.Doing the expected sum and subtracting the actual gives the run time of O(2n), however a bucket sort will almost always do it in less time (somewhere between O(n) and O(2n)): 1. create a 101-int (or boolean) array (to have a 100-index) 2. traverse original and for each int, assign value in bucket array to 1 or true. 3.After first traversal, traverse created array starting at one, and when value is false, print it.100100 coz in array it initial value starts frm 0 to 100. or else 4 further clarification u can study array chapter in c or c++100Show More ResponsesThe question: "An array of 99 elements contains integers from 1 to 100 with one missing element. Find the missing element." The information states that the integer count is 1 to 100. I take this to be inclusive of all elements in the array so that the missing inters would be subjective to their arrangement or random. In other words, I do not have enough information to say which one.1I need more information. 1. Are the integers unique in this array? 2. Do I have enough information to find the sum of the integers in the array (or some aggregation)? If sum is available, then, the answer is 5050-sum{integers}.Bucket Sort works and summation works. I think both are good, practical and clever solutions. I think sorting the array then searching may be unnecessary computation. Another interesting method which may be faster. SIMD computers may do this particularly quickly: Do a bitwise operation on all the elements: Result = Array[0] xor Array[1] xor ... Array[98] xor 1 xor 2 xor ... xor 100 Result = Missing number. Explanation: When you xor 2 identical numbers your result = 0. For example, 5 xor 5 -> 101 xor 101 = 000. (5 in decimal is 101 in binary). Knowing that "xoring" 2 identical numbers results in zero is useful. Now we apply this useful info to the problem. Array is Identical to a list of 1,2,3,...,100 except for one number. In other words 1,2,3,...,100 duplicates all of array's elements and adds one extra element that is missing in Array. Therefore, we now have 2 instances of each element in the Array in addition to one extra element in 1,2,3,...,100. We can see when you xor two duplicate numbers you get zero. Because we have pairs for all numbers in Array and one extra number we are essentially "xoring" the missing number with zero. When we xor the missing number with zero we get the missing number. (For example, 6 xor 0 -> 110 xor 000 = 110)The question states that one (not two or three or n) element ("value") from 1 to 100 is missing. There are 99 elements ("values") in the array. The question implies that the data is well-formed because it states that only element is missing. It doesn't ask you to find the missing value(s), but the one (singular) missing element. With the problem constrained, the solution falls out. Subtracting from 5050 is an elegant solution, but not obvious as to why it works. The array of booleans is more obvious, but doesn't scale well.I agree with one of the answers in this thread...5050-sum(elements) = missing item. Other approach that crossed my mind is something similar to binary search. Check the index of 50th element: if A(50) == 50, the missing element > 50, else if A(50) > 50, missing element <50. Do this iteratively. The number of comparisons would be log 100 = 7.Add 1-100 to a hash of 100 elements. Then compare each element with the hash.. Answer in o(n)Show More ResponsesShow More ResponsesShow More ResponsesShow More ResponsesShow More ResponsesShow More ResponsesShow More ResponsesShow More ResponsesShow More ResponsesShow More ResponsesShow More Responses One or more comments have been removed. 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### Senior Software Engineer at Facebook was asked...

Jul 18, 2010
 Write some pseudo code to raise a number to a power.11 Answerspretty trivial...int raise(num, power){ if(power==0) return 1; if(power==1) return num; return(raise(num, power-1)*num); }double Power(int x, int y) { double ret = 1; double power = x; while (y > 0) { if (y & 1) { ret *= power; } power *= power; y >>= 1; } return ret; }Show More ResponsesIn Ruby: def power(base, power) product = 1 power.times do product *= base end product end puts "2^10 = 1024 = #{power(2,10)}" puts "2^0 = 1 = #{power(2,0)}" puts "2^1 = 2 = #{power(2,1)}"If I were an interviewer, I would ask the Aug 29, 2010 poster why he used bitwise operators, and whether he would deploy that code in a production environment, or if he merely wanted to demonstrate, for purposes of the interview, that he understands bitwise operations.Because it uses dynamic programming and is lots more efficient than your algorithm.If the power is not integer, use ln and Taylor seriesIf I'm the interviewer, none of above answers is acceptable. What if y < 0? what if y < 0 and x == 0? I'm seeing an endless recursion that will eventually overflow the stack, and the none-recursive one just simply returns 1.There is a way to do this in a logN way rather than N. function power(x, n) { if n == 1 return x; // Even numbers else if (n%2 == 0) return square( power (x, n/2)); // Odd numbers else return power(x, n-1); } This is from Programming pearls.. interesting way.small mistake function power(x, n) { if n == 1 return x; // Even numbers else if (n%2 == 0) return square( power (x, n/2)); // Odd numbers else return power(x, n-1) * x; }# Solution for x ^ n with negative values of n as well. def square(x): return x * x def power(x, n): if x in (0, 1): return x if n == 0: return 1 if n < 0: x = 1.0 / x n = abs(n) # Even number if n % 2 == 0: return square(power(x, n/2)) # Odd number else: return x * power(x, n - 1) print ("0 ^ 0 = " + str(power(0, 0))) print ("0 ^ 1 = " + str(power(0, 1))) print ("10 ^ 0 = " + str(power(10, 0))) print ("2 ^ 2 = " + str(power(2, 2))) print ("2 ^ 3 = " + str(power(2, 3))) print ("3 ^ 3 = " + str(power(3, 3))) print ("2 ^ 8 = " + str(power(2, 8))) print ("2 ^ -1 = " + str(power(2, -1))) print ("2 ^ -2 = " + str(power(2, -2))) print ("2 ^ -8 = " + str(power(2, -8)))

### Senior Software Engineer at Google was asked...

Sep 6, 2010
 Given an array of numbers, replace each number with the product of all the numbers in the array except the number itself *without* using division. 8 AnswersO(size of array) time & space: First, realize that saying the element should be the product of all other numbers is like saying it is the product of all the numbers to the left, times the product of all the numbers to the right. This is the main idea. Call the original array A, with n elements. Index it with C notation, i.e. from A[0] to A[n - 1]. Create a new array B, also with n elements (can be uninitialized). Then, do this: Accumulator = 1 For i = 0 to n - 2: Accumulator *= A[i] B[i + 1] = Accumulator Accumulator = 1 For i = n - 1 down to 1: Accumulator *= A[i] B[i - 1] *= Accumulator Replace A with B It traverses A twice and executes 2n multiplicates, hence O(n) time It creates an array B with the same size as A, hence O(n) temporary space# A Python solution (requires Python 2.5 or higher): def mult(arr, num): return reduce(lambda x,y: x*y if y!=num else x, arr) arr = [mult(arr,i) for i in arr] # O(n^2) time, O(n) spaceCreate two more arrays. One array contains the products of the elements going upward. That is, B[0] = A[0], B[1] = A[0] * A[1], B[2] = B[1] * A[2], and so on. The other array contains the products of the elements going down. That is, C[n] = A[n], C[n-1] = A[n] * A[n-1], and so on. Now A[i] is simply B[i-1] * C[i+1].Show More Responsesdef without(numbers): lognums = [math.log10(n) for n in numbers] sumlogs = sum(lognums) return [math.pow(10, sumlogs-l) for l in lognums]Here are my 2 cents to do this in memory without creating temporary arrays. The simple solution , if division was allowed, was multiple all the elements of the array i.e. tolal = A[0]*A[1]]*....*A[n-1] now take a loop of array and update element i with A[i] = toal/A[i] Since division is not allowed we have to simulate it. If we say X*Y = Z, it means if X is added Y times it is equal to Z e.g. 2*3 = 6, which also means 2+2+2 = 6. This can be used in reverse to find how mach times X is added to get Z. Here is my C solution, which take pointer to array head A[0] and size of array as input void ArrayMult(int *A, int size) { int total= 1; for(int i=0; i< size; ++i) total *= A[i]; for(int i=0; i< size; ++i) { int temp = total; int cnt = 0; while(temp) { temp -=A[i]; cnt++; } A[i] = cnt; } } Speed in O(n) and space is O(1)#include #define NUM 10 int main() { int i, j = 0; long int val = 1; long A[NUM] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; // Store results in this so results do not interfere with multiplications long prod[NUM]; while(j < NUM) { for(i = 0; i < NUM; i++) { if(j != i) { val *= A[i]; } } prod[j] = val; i = 0; val = 1; j++; } for(i = 0; i < NUM; i++) printf("prod[%d]=%d\n", i, prod[i]); return 0; }void fill_array ( int* array, size ) { int i; int t1,t2; t1 = array[0]; array[0] = prod(1, size, array ); for(i = 1; i < size; i++){ t2 = array[i]; array[i] = prod(i, array.size(), array)*t1; t1 *= t2; } int prod(start, end, array){ int i; int val(1); for(i = start; i < end; i++ ) val *= array[i]; return val; } One or more comments have been removed. Please see our Community Guidelines or Terms of Service for more information.

### Machine Learning Software Engineer at Facebook was asked...

Jan 21, 2010
 Suppose you have a matrix of numbers. How can you easily compute the sum of any rectangle (i.e. a range [row_start, row_end, col_start, col_end]) of those numbers? How would you code this?8 AnswersIt can be done in constant time by precalculating sums of some basic rectangles (extending all the way to the border of the matrix). That precalculation times time O(n) by simple dynamic programming.Please elaborate, which "basic rectangles"? Are you recursively dividing each rectangle into 4 smaller rectangles? Precalc time for doing that is not O(n)?!?Compute the sum of the rectangles, for all i,j, bounded by (i,j), (i,m), (n,j), (n,m), where (n,m) is the size of the matrix M. Call that sum s(i,j). You can calculate s(i,j) by dynamic programming: s(i,j) = M(i,j) + s(i+1,j) + s(i,j+1) - s(i+1,j+1). And the sum of any rectangle can be computed from s(i,j).Show More ResponsesAwesome!!The answer is already popular in computer vision fields!! It is called integral imaging. See this page http://en.wikipedia.org/wiki/Haar-like_featuresLet a[][] be the 2d array, int i=0; for( j = row_start; j <= row_end; j++) for( k = col_start; k <= col_end; k++) i+=a[j][k];Iterate over matrix as an array storing (new sums array) in each position the cumulative sum up to that point. For each row in the desired submatrix we can compute its sum as a difference between its end and start positions. Repeat for other rows. Add up all the row sums. One or more comments have been removed. Please see our Community Guidelines or Terms of Service for more information.

### Senior Software Engineer at Google was asked...

Mar 19, 2009
 What sort would you use if you required tight max time bounds and wanted highly regular performance.6 AnswersVector sort.Guaranteed to be O(n log n) performance. No better, no worse.That is so say, a "Balanced Tree Sort" is guaranteed to be O(n log n) always.Show More ResponsesMerge sort and heapsort are always guaranteed to be n*log(n). Quicksort is usually faster on the average but can be as bad as O(n^2), although with very low probability. Heapsort also does it sorting in-place, without needing an extra buffer, like mergesort. Lastly, heapsort is much easier to implement and understand than balancing trees mentioned by earlier posts.for something like this you generally want bubble sort or insertion sort. It's not about being fast it's about being consistent. Make it do exactly the same thing every time.Use a sorting network. There's some precomputation time, but runtime will be very consistent (the only variability is branch prediction performance)

### Front End Web Developer at Bloomberg L.P. was asked...

Feb 23, 2010
 What is a JavaScript callback function?5 Answers5 vote down star 4 I understand passing in a function to another function as a callback and having it execute, but I'm not understanding the best implementation to do that. I'm looking for a very basic example, like this: var myCallBackExample = { myFirstFunction : function( param1, param2, callback ) { // Do something with param1 and param2. if ( arguments.length == 3 ) { // Execute callback function. // What is the "best" way to do this? } }, mySecondFunction : function() { myFirstFunction( false, true, function() { // When this anonymous function is called, execute it. }); } }; In myFirstFunction, if I do return new callback(), then it works and executes the anonymous function, but that doesn't seem like the correct approach to me.I don't think Bloomberg is a very good company. I am an excellent web developer and have gotten multiple offers from other companies with big names, but was rejected by Bloomberg. They are too demanding during the job interview and it becomes a game of how well you can interview as opposed to how talented an employee you are and how much you can contribute to the growth of the company.A callback function is a piece of JavaScript code that executes after the main function that the callback is attached to executes successfully.Show More Responsesudaykanth, I would say that a .forEach() would be the most common and most basic use of a callback function. I'm just writing this to help anyone that might have a hard time thinking up a quick example if the come across this question themselves. Example: var numArray = [ 1, 2, 3 ] ; numArray.forEach( function( i ) { console.log( arr[ i - 1 ] ) } ) ; // logs out // 1 // 2 // 3Is there a front end role at bloomberg. I guess your position must have been labelled software dev right? altho ur a dront end dev

### IT Developer at FDM Group was asked...

Dec 9, 2010
 How many unique handshakes if each person in a group of 10 give handshakes out to each and every other individual. (a) 100 (b) 50 (c) 45 (d) 20 (e) 105 Answers45. Imagine it as a polygon of side 10. Or draw out triangle, square, pentagon, and see the pattern yourself, if you don't know the algorithm.true, or 9+8+7+...+2+1Or just do: (10 Combination 2) = 10!/(2!8!) = 45Show More Responsesn(n+1)/2 Where n =9 Answer: 45 One or more comments have been removed. Please see our Community Guidelines or Terms of Service for more information.

### Junior Java Developer at Insight Global was asked...

Nov 15, 2012
 Implement a method to determine whether a string is a palindrome.4 AnswersRecursive method; start from the ends and work your way in. Use indices if worried about memory.Take a string as function parameter. Copy this str value into a new var, then use .reverse() thereupon. Compare the reversed copy back against original string using turnery operator to set resVariable to "true" : "false". Return resVariable.(Using .split(""), as well as .join(""))Show More Responsesconst palindrome = (str) => str == str.reversed() palindrome('hello') // false palindrome('eve') // true

### Software Engineer In Test at Google was asked...

Mar 18, 2009
 Implement a binary tree and explain it's function4 AnswersBinary Search tree is a storage data structure that allows log(n) insertion time, log(n) search, given a balanced binary search tree. The following implementation assumes an integer bst. There's a million implementations. Just look on wikipedia for search and insert algorithms.Hi Xin Li, A binary tree is not the same as binary search tree.. A binary tree is a tree in which every node has atmost two children nodes. It is a k-ary tree in which k=2. A complete binary tree is a tree in which all nodes have the same depth.The fact is ttttttt t t. T to t. To. A a aaAs Sdsassss.Show More Responses One or more comments have been removed. Please see our Community Guidelines or Terms of Service for more information.
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