给你一个字符串s,输出s能够组成的所有不同的字符串

编程实现：给你一个字符串s,输出s能够组成的所有不同的字符串.
如：s="abc",
输出：abc,acb,bac,bca,cba,cab

package DataStructre;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;

/**
 * 编程实现：给你一个字符串s,输出s能够组成的所有不同的字符串.
 * 如：s="abc",
 * 输出：abc,acb,bac,bca,cba,cab
 */
public class Ans {
    public static void main(String[] args) {
        String s = "abc";
        String s2 = "abcbe";
        List<String> res = permutation(s);
        for (int i = 0; i < res.size(); i++) {
            System.out.println(i + ": " + res.get(i));
        }
        System.out.println("=======");
        List<String> res2 = permutation(s2);
        for (int i = 0; i < res2.size(); i++) {
            System.out.println(i + ": " + res2.get(i));
        }
    }

    public static List<String> permutation(String s) {
        List<String> res = new ArrayList<>();
        char[] c = s.toCharArray();
        dfs(c, 0, res);
        System.out.println(res);
        return res;
    }

    static void dfs(char[] c, int start, List<String> res) {
        if (start == c.length - 1) {
            res.add(String.valueOf(c));
            return;
        }
        HashSet<Character> set = new HashSet<>();
        for (int i = start; i < c.length; i++) {
            if (set.contains(c[i])) continue;
            set.add(c[i]);
            swap(c, i, start);
            dfs(c, start + 1, res);
            swap(c, i, start);
        }
    }

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