[LeetCode 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.

Diffculty
Medium

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Analysis

class Solution { public: vector letterCombinations(string digits) { int n = digits.length(); if(n <= 0) return vector(); vector lettComb; string dict[] = {"", " ", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"}; string comb(n,'\0'); findLettComb(digits, 0, dict, comb, lettComb); return lettComb; }

void findLettComb(string &digits, int index, string dict[], string &comb, vector<string> &lettComb) {
    if(index == digits.size()) {
        lettComb.push_back(comb);
        return;
    }

    string lett = dict[digits[index] - '0'];
    for(int i = 0; i < lett.length(); i++) {
        comb[index] = lett[i];
        findLettComb(digits, index+1, dict, comb, lettComb);
    }
}

};