LeetCode-017：Letter Combinations of a Phone Number

最新推荐文章于 2020-09-11 09:49:19 发布

原创最新推荐文章于 2020-09-11 09:49:19 发布 · 170 阅读

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#DFS #回溯

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本文介绍了一个经典的编程问题：给定一个仅包含数字2-9的字符串，返回所有可能的字母组合。文章详细解释了问题背景，给出了一个使用深度优先搜索(DFS)和回溯算法的C++解决方案。

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题目：

Given a string containing digits from 2-9 inclusive, 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. Note that 1 does not map to any letters.

Example:

Input: "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.

题意：

还用得着解释？

思路：

DFS+回溯一波走~

Code：

class Solution {
public:
    string g[11]={"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
    vector<string> letterCombinations(string digits) {
        vector<string> q;
        if(digits.length()==0) return q;
        string s;
        dfs(q,s,digits,0);
        return q;
    }
    void dfs(vector<string> &q,string &s,string &digits, int cur) {
		if(cur>=digits.length()){
			q.push_back(s);
			return;
		}
        int t=digits[cur]-'0';
		for(int i=0;i<g[t].length();i++){
            char ch=g[t][i];
			s.push_back(ch);
			dfs(q,s,digits,cur+1);
			s.pop_back();
		}
	}
};