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Implement a Sudoko puzzle validator - given a 9x9 matrix of numbers (1-9) and "." for empty spaces, return true for a valid puzzle matrix and false if it would not be a valid sudoku puzzle.

4 Answers

I basically just checked for duplicate numbers in each row, column, and then each 3x3 inner matrix. each iteration, i reset a dictionary of "seen" numbers. "." characters wouldn't matter, if i saw a number 1-9 i would check if it was already in the dictionary, if it was return false. return true at the very end if never encountered repeat numbers in rows, columns, or inner squares. when I explained this approach to the interviewer and he seemed satisfied with it although it was not easy to tell what the hell he was thinking or saying. i was working in a shared text file (i think it was codepen?), and even though the interviewer could have typed too, he didn't (even when i had to ask him repeatedly to spell a word i couldn't make out)..

Each iteration? You need just an iteration. Complexity o(n).

my solution was still O(n) - 3n to be exact. i "iterate" over the entire matrix 3 times - once to check for duplicates in the rows, once to check for duplicates in the columns, and once to check for duplicates within sub matrices. During each of those iterations I visit each element of the matrix exactly once and just check whether it's already in a dictionary of seen numbers which would be a constant time operation, so this is in total would be O(n). I can't think of how to check all those in just one iteration , if that's what you were saying you could do. (at least without using O(n) extra space.. mine only uses constant extra space) i would appreciate if you could elaborate

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Algorithms question was probably the trickiest thing. Given an array of integers of length N from 1 to N-1, how would you detect a single duplicate in the array?

3 Answers

What's the angle between the hands of a clock if the time is 3:15.

3 Answers

Hardest Q was: Here's a binary tree: find the longest path within it. So, find a path between any two leaf nodes, where the path is the longest.

3 Answers

2nd skype: - Lets say you have to build an activity (screen) which has a drop-down & once you select an item in the drop-down, it loads an image corresponding to that on the screen below. - How will handle cases where user is very rapidly changing his selection from the drop down

2 Answers

dispatch queues … what are they and how do they work?

2 Answers

If one has a collection of N stock options vesting over P periods, describe algorithmically how one would come up with the data for a table listing how many options are awarded per period.

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Given a tree with potentially multiple child nodes, write an algorithm that describes how you would completely reverse (or mirror image) the tree. That is, given a tree with a root node of A and three children, BCD, and two children of B named EF, he wanted to generate a new tree that looked like a root node of A, then DCB with "FE" being the reversed children under B.

2 Answers

You are in a game of Russian Roulette with a revolver that has 3 bullets placed in three consecutive chambers. The cylinder of the gun will be spun once at the beginning of the game. Then, the gun will be passed between two players until it fires. Would you prefer to go first or second?

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given a matrix where the numbers ascend both in rows & columns, e.g. 1 3 5 7 9 11 13 15 18 20 22 24 26 28 30 31 33 36 38 39 42 44 47 49 50 If you're asked to write a function that provides a boolean (YES or NO) answer to "does this number exist in this matrix", explain how you would design an algorithm to be most optimal.

2 Answers
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