# 电话号码的字母组合

**电话号码的字母组合**

给定一个仅包含数字 2-9 的字符串，返回所有它能表示的字母组合。给出数字到字母的映射如下（与电话按键相同）。注意 1 不对应任何字母。

```javascript
var letterCombinations = function(digits) {
    if(!digits) return [];
    let map = {
        '2': 'abc','3':'def','4':'ghi','5':'jkl','6':'mno','7':'pqrs','8':'tuv','9':'wxyz'
    };
    let res = [];
    function dfs(index,path) {
        if(index === digits.length) {
            res.push(path);
            return;
        }
        for (let i = 0;i < map[digits[index]].length;i++) {
            path += map[digits[index]][i];
            dfs(index+1,path.slice());
            path = path.slice(0, path.length-1);
        }
    }
    dfs(0,'');
    return res;
};

```


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