leetcode 017 —— Letter Combinations of a Phone Number

自犬邦

于 2015-07-09 10:33:20 发布

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本文介绍了一种使用回溯法解决电话号码对应字母的所有可能组合的问题。通过递归地构建字符串来生成所有可能的组合，利用电话按键上的字母映射表进行匹配。

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"].

思路：简单的回溯法

class Solution {
public:
	vector<string> letterCombinations(string digits) {
		vector<string> table={"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
		vector<string> res;
		if (digits.empty()) return res;
		scan(0, "", digits, table, res);
		return res;

	}
	void scan(int level, string path, string &digits, vector<string> &table,vector<string> &res){
		if (level == digits.size()){
			res.push_back(path);
			return;
		}
		for (int i = 0; i < table[digits[level] - '0'].size(); i++){
			path.push_back(table[digits[level] - '0'][i]);
			scan(level + 1, path, digits, table, res);
			path.pop_back();
		}
	}
};