#yyds干货盘点# LeetCode程序员面试金典：无重复字符串的排列组合

题目：

无重复字符串的排列组合。编写一种方法，计算某字符串的所有排列组合，字符串每个字符均不相同。

示例1:

输入：S = "qwe"

输出：["qwe", "qew", "wqe", "weq", "ewq", "eqw"]

示例2:

输入：S = "ab"

输出：["ab", "ba"]

代码实现：

class Solution {
    List<String> list = new ArrayList<>();

    public String[] permutation(String S) {
        permutate(S.toCharArray(), 0);
        String[] res = new String[list.size()];
        for (int i = 0; i < res.length; i++) {
            res[i] = list.get(i);
        }
        return res;
    }

    public void permutate(char[] arr, int first) {
        if (first == arr.length - 1) {
            list.add(new String(arr));
            return;
        }
        for (int i = first; i < arr.length; i++) {
            swap(arr, first, i);
            permutate(arr, first + 1);
            swap(arr, first, i);
        }
    }

    public void swap(char[] arr, int i, int j) {
        char temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }
}