[数据结构与算法]JS力扣刷题 93. 复原 IP 地址

var restoreIpAddresses = function(s) {
    let answers = [];
    let answer = [];
    function backtrack(index, start){
        if(index == 4)//走到最后一层
            if(start == s.length){//走到了最后一个字符
                answers.push(answer.join('.'));
                return;
            }
            else
                return;
        let i = start;
        //将一个字符放入解
        if(i < s.length){
            answer.push(s[i]);
            backtrack(index + 1, i + 1);
            answer.pop();
        }
        //将两个字符放入解
        if(i + 1 < s.length && Number(s[i] + s[i + 1]) >= 10){
            answer.push(s[i] + s[i + 1]);
            backtrack(index + 1, i + 2);
            answer.pop();
        }
        //将三个字符放入解
        if(i + 2 < s.length && Number(s[i] + s[i + 1] + s[i + 2]) >= 100 &&Number(s[i] + s[i + 1] + s[i + 2]) <= 255){
            answer.push(s[i] + s[i + 1] + s[i + 2]);
            backtrack(index + 1, i + 3);
            answer.pop();
        }
    }
    backtrack(0,0);
    return answers;
};

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