17. Letter Combinations of a Phone Number（js）

17. Letter Combinations of a Phone Number

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"].
题意：找到按键对应数字所有的字符组合
代码如下:

var letterCombinations = function(digits) {
    //结果数组
    let res=[];
    let charArr=["0","1","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"];
    back(res,digits,"",0,charArr);
    return res;
};
//回溯
var back=function(res,digits,curr,index,charArr){
    if(index===digits.length){
        if(curr.length!==0) res.push(curr);
        return ;
    }
    //找到数字对应的字符串
    let temp=charArr[parseInt(digits.charAt(index))];
    for(let i=0;i<temp.length;i++){
        let next=curr+temp.charAt(i);
        back(res,digits,next,index+1,charArr);
    }
};