JAVA 实现全排列和组合

import java.util.LinkedList;
import java.util.List;
import java.util.Scanner;

public class Main {

public static void arrange(String s, List<Integer> list) {
if (list.size() == 0) {
System.out.println(s);
} else {
for (int i = 0; i < list.size(); ++i) {
List<Integer> temp = new LinkedList<>(list);
//取出一个数，剩下的数进行全排列
Integer remove = temp.remove(i);
arrange(s + remove, temp);
temp = null;
}
}
}

public static void group(String s, List<Integer> list, int n) {
if (n == 0) {
System.out.println(s);
} else {
for (int i = 0; i < list.size(); ++i) {
Integer integer = list.get(i);
int length = s.length();
//限定前面的数比后面的小，用来去重复，例如 1 2 和2 1
if(length != 0 && s.charAt(length - 1) > integer + '0'){
continue;
}
List<Integer> temp = new LinkedList<>(list);
Integer remove = temp.remove(i);
group(s + remove, temp, n - 1);
temp = null;
}
}
}

public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
List<Integer> list = new LinkedList<>();
for (int i = 1; i <= n; ++i) {
list.add(i);
}
arrange("", list);
System.out.println();
group("", list, 2);
System.out.println();
}
}

public static void swap(List<Integer> list, int i, int j){
Integer src = list.get(i);
Integer dst = list.get(j);
Integer temp = src;
src = dst;
dst = temp;
}

public static void arrange2(String s, List<Integer> list, int start) {
if (start == list.size()) {
System.out.println(s);
} else {
for (int i = start; i < list.size(); ++i) {
swap(list, start, i);
arrange2(s + list.get(start), list, start + 1);
swap(list, start, i);
}
}
}