Leetcode题解-17. Letter Combinations of a Phone Number
2017-10-12 16:02
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Leetcode题解-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.
思路
这道题思维比较简单,就是不断扩展字符串的长度,每次扩展形成的字符串是原来的三或四倍。代码
vector<string> letterCombinations(string digits) { if(digits.empty()) return vector<string>(); char letters[8][4] = {{'a','b','c'},{'d','e','f'},{'g','h','i'},{'j','k','l'},{'m','n','o'},{'p','q','r','s'},{'t','u','v'},{'w','x','y','z'}}; int l = digits.size(); vector<string> res; res.push_back(""); for(int i = 0; i < l; i++){ vector<string> tem; int count; if(digits[i] == '7' || digits[i] == '9') count = 4; else if(digits[i] > '1' && digits[i] < '9') count = 3; else break; for(int j = 0; j < count; j++){ vector<string>::iterator it; for(it = res.begin(); it < res.end(); it++){ tem.push_back((*it) + letters[digits[i] - '2'][j]); } } res.swap(tem); } return res; }
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