eBay

www.ebayinc.com
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## Interview Question

Interview San Jose, CA

# write code to do the reverse mapping from phone number to

its all possible combination of letters. Ex- if dialed 12 then all possible combinations will be ad, ae, af, bd, be, bf, cd, ce, cf and so on...
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interviewer was not at all helpful, seems like she didn't know what I was talking about

Interview Candidate on Sep 2, 2012
1

This is a permutation problem. Each number maps to 3 or 4 letters, except zero, which does not map to anything. Create map of each number to an array of characters: ncMap.get(1) returns {A,B,C} Let int[] input be the phone number. int print(int[] input, int inputStartPos, HashMap<Integer,Character[]> ncMap, List<Character> accumulator){ if(input == null || inputStartPos < 0 || inputStartPos > input.length-1) return -1; Character[] chars = ncMap.get(input[inputStartPos]); if(inputStartPos == input.length-1){ for(int i = 0; i < chars.length; i++){ printAccumulator(accumulator); // print all chars we have so far. print(chars[i]); } return 0; // success } else { for(int i = 0; i < chars.length; i++){ accumulator.append(chars[i]); print(input, inputStartPos++, ncMap, accumulator); } } }

Anonymous on Nov 12, 2012