题目描述

输入一个字符串,按字典序打印出该字符串中字符的所有排列。例如输入字符串 abc，则打印出由字符 a,b,c 所能排列出来的所有字符串 abc,acb,bac,bca,cab和cba
f
题目链接：https://www.nowcoder.com/practice/fe6b651b66ae47d7acce78ffdd9a96c7

解题思路

1. 递归法（回溯）
2. 迭代法（字典生成）[后续更新]

import java.util.ArrayList;
import java.util.Collections;

public class Solution {
    public ArrayList<String> Permutation(String str) {
        ArrayList<String> result = new ArrayList<>();
        rec(str.toCharArray(), 0, result);
        Collections.sort(result);
        return result;
    }
    
    private void rec(char[] chr, int i, ArrayList<String> result) {
        if (i == chr.length - 1) {
            String value = String.valueOf(chr);
            if (!result.contains(value)) {
                result.add(value);
            }
        } else {
            for (int j = i; j < chr.length; j++) {
                swap(i, j, chr);
                rec(chr, i+1, result);
                swap(i, j, chr);
            }
        }
    }
    
    private void swap(int i, int j, char[] chr) {
        char tmp = chr[i];
        chr[i] = chr[j];
        chr[j] = tmp;
    }
}