Java实现字符串的全排列

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package com.leetcode;import java.util.ArrayList;public class Permutation {public static void main(String[] args) {ArrayList<String> res = perms2("abc");System.out.println(res);}//法一：public static ArrayList<String> perms1(String s){ArrayList<String> res = new ArrayList<String>();if(s == null)return null;if(s.isEmpty()){res.add("");return res;}for(int i = 0; i < s.length(); i++){char c = s.charAt(i);String start = s.substring(0, i);String end = s.substring(i + 1);ArrayList<String> words = perms1(start + end);for(String word : words){String newStr = c + word;res.add(newStr);}}return res;}//法二：public static ArrayList<String> perms2(String s){ArrayList<String> res = new ArrayList<String>();if(s == null)return null;if(s.isEmpty()){res.add("");return res;}char c = s.charAt(0);String reminder = s.substring(1);ArrayList<String> words = perms2(reminder);for(String word : words){for(int i = 0; i <= word.length(); i++){String newStr = insertCharAt(word, c, i);res.add(newStr);}}return res;}public static String insertCharAt(String s, char c, int i){String start = s.substring(0, i);String end = s.substring(i);return start + c + end;}}

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