【LeetCode算法练习（C++）】Letter Combinations of a Phone Number

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题目：
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”].

链接：Letter Combinations of a Phone Number

解法：暴力循环。时间O(n^m)

class Solution {
public:vector<string> letterCombinations(string digits) {vector<string> bot;vector<string> ans;vector<string> tmp;bot.push_back("");bot.push_back("");bot.push_back("abc");bot.push_back("def");bot.push_back("ghi");bot.push_back("jkl");bot.push_back("mno");bot.push_back("pqrs");bot.push_back("tuv");bot.push_back("wxyz");for (int i = 0; i < bot[digits[0] - '0'].size(); i++) {char c = bot[digits[0] - '0'][i];string str;stringstream stream;stream << c;str = stream.str();ans.push_back(str);}for (int i = 1; i < digits.length(); i++) {tmp = ans;ans.clear();for (int k = 0; k < tmp.size(); k++) {for (int j = 0; j < bot[digits[i] - '0'].size(); j++) {ans.push_back(tmp[k] + bot[digits[i] - '0'][j]);}}}return ans;}
};

Runtime: 3 ms

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