Java实现全排列的三种算法详解

import java.util.ArrayList;
import java.util.List;
 
public class h618_1 {
 
    static List<List<Integer>> res = new ArrayList<>();
    public static void main(String[] args) {
        int[] arr = {1,2,3};
 
        h618_1 h1 = new h618_1();
        h1.dfs(arr,new ArrayList<>());
        for (List<Integer> re : res) {
            System.out.println(re);
        }
 
    }
 
    public List<List<Integer>> dfs( int[] arr,List<Integer> list){
        List<Integer> temp = new ArrayList<>(list);
        if (arr.length == list.size()){
            res.add(temp);
        }
        for (int i=0;i<arr.length;i++){
            if (temp.contains(arr[i])){
                continue;
            }
            temp.add(arr[i]);
            dfs(arr,temp);
            temp.remove(temp.size()-1);
        }
        return res;
    }
 
}

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
 
public class h618_2 {
    static List<List<Integer>> res = new ArrayList<>();
    public static void main(String[] args) {
 
        int[] arr = {1,2,3};
        h618_2 h2 = new h618_2();
        h2.pailie_swap(0,arr);
 
    }
    public void pailie_swap(int index, int[] arr){
        if (arr.length==index){
            System.out.println(Arrays.toString(arr));
            return;
        }
        for (int i = index;i<arr.length;i++){
            swap(i,index,arr);
            pailie_swap(index+1,arr);
            swap(i,index,arr);
        }
 
    }
 
    public void swap(int i,int j ,int[] arr){
        int temp = arr[j];
        arr[j] = arr[i];
        arr[i] = temp;
 
    }
}

import java.util.ArrayList;
 
public class h618_3 {
 
    public static void main(String[] args) {
        String aa = "123";
        h618_3 h3 = new h618_3();
        ArrayList<String> res = new ArrayList<>();
        res = h3.getPermutation0(aa);
 
        for (String re : res) {
            System.out.println(re);
        }
 
    }
 
    public ArrayList<String> getPermutation0(String A) {
        int n = A.length();
        ArrayList<String> res = new ArrayList<>();
        res.add(A.charAt(0) + "");//初始化,包含第一个字符
 
        for (int i = 1; i < n; i++) {//第二个字符插入到前面生成集合的每个元素里面
            ArrayList<String> res_new = new ArrayList<>();
            char c = A.charAt(i);//新字符
            for (String str : res) {//访问上一趟集合中的每个字符串
                //  插入到每个位置,形成一个新串
                String newStr = c + str;//加在前面
                res_new.add(newStr);
                newStr = str + c;//加在后面
                res_new.add(newStr);
                //加在中间
                for (int j = 1; j < str.length(); j++) {
                    newStr = str.substring(0, j) + c + str.substring(j);
                    res_new.add(newStr);
                }
            }
            res = res_new;//更新
 
        }
        return res;
    }
}