2017-09-10 LeetCode_017 Letter Combinations of a Phone Number

17. Letter Combinations of a Phone Number

Given a digit string, return all possible letter combinations that the number could represent.

A mapping of digit to letters (just like on the telephone buttons) is given below.

Input:Digit string "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

Note:
Although the above answer is in lexicographical order, your answer could be in any order you want.

Solution:

vector<string> myans;

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string sw[10] = {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};

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class Solution {

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public:

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    void deep(string & digits, int step, string now) {

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        if (digits.length() == 0) return;

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        if (step == digits.length()) {

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            myans.push_back(now); return;

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        }

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        for (int i = 0; i < sw[digits[step]-'0'].length(); i++)

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            deep(digits, step+1, now+sw[digits[step]-'0'][i]);

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    }

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    vector<string> letterCombinations(string digits) {

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        myans.clear();

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        deep(digits, 0, "");

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        return myans;

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    }

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};