字符串的全排列

方法一：使用 js 中的 reduce 方法

function allPermutation(str) {
    if (str.length === 2) {
        return [str, str[1] + str[0]];
    }
    return str.split('').reduce((acc, val, idx) =>
        acc.concat(allPermutation(str.slice(0, idx) + str.slice(idx + 1)).map(v => val + v)), []);
}
console.log(allPermutation('abc'));
//输出 ["abc", "acb", "bac", "bca", "cba", "cab"]

方法二：交换字符串中的值

function allPermutation(strArr, left, right, arr) {
    if (left > right) {
        return;
    } else if (left === right) {
        arr.push(strArr.join(''));
    } else {
        for (let i = left; i <= right; i++) {
            [strArr[left], strArr[i]] = [strArr[i], strArr[left]];
            allPermutation(strArr, left + 1, right, arr);
            [strArr[i], strArr[left]] = [strArr[left], strArr[i]];
        }
    }
    return arr;
}
let arr = [],
    strArr = ['a', 'b', 'c'];
console.log(allPermutation(strArr, 0, strArr.length - 1, arr));
//输出 ["abc", "acb", "bac", "bca", "cba", "cab"]