Java 实现排列组合

import java.util.ArrayList;

public class Pailiezuhe {
    public static void main(String[] args) {
        ArrayList<Integer> list = new ArrayList<>();
        int[] shu = new int[]{1, 2, 3, 4};
        //可重复选，4选3的全排列
        kechongfuxuanpailie(shu, list, 3, 0);
        System.out.println("*******************");
        //不可重复选，4选3的全排列
        bukechongfuxuanpeilie(shu, list, 3, 0);
        System.out.println("*******************");
        //4选3的组合方式
        zuhe(shu, list, 3, 0, 0);

    }

    public static void kechongfuxuanpailie(int[] shu, ArrayList<Integer> list, int tag, int cur) {
        if (cur == tag) {
            System.out.println(list);
            return;
        }
        for (int i : shu) {
            list.add(i);
            kechongfuxuanpailie(shu, list, tag, cur + 1);
            list.remove(list.size() - 1);
        }
    }


    public static void bukechongfuxuanpeilie(int[] shu, ArrayList<Integer> list, int tag, int cur) {
        if (cur == tag) {
            System.out.println(list);
            return;
        }
        for (int i : shu) {
            if (!list.contains(i)) {
                list.add(i);
                bukechongfuxuanpeilie(shu, list, tag, cur + 1);
                list.remove(list.size() - 1);
            }
        }
    }

    public static void zuhe(int[] shu, ArrayList<Integer> list, int tag, int has, int cur) {
        if (has == tag) {
            System.out.println(list);
            return;
        }
        for (int i = cur; i < shu.length; i++) {
            if (!list.contains(shu[i])) {
                list.add(shu[i]);
                zuhe(shu, list, tag, has + 1, i);
                list.remove(list.size() - 1);
            }
        }
    }
}

运行结果

[1, 1, 1]
[1, 1, 2]
[1, 1, 3]
[1, 1, 4]
[1, 2, 1]
[1, 2, 2]
[1, 2, 3]
[1, 2, 4]
[1, 3, 1]
[1, 3, 2]
[1, 3, 3]
[1, 3, 4]
[1, 4, 1]
[1, 4, 2]
[1, 4, 3]
[1, 4, 4]
[2, 1, 1]
[2, 1, 2]
[2, 1, 3]
[2, 1, 4]
[2, 2, 1]
[2, 2, 2]
[2, 2, 3]
[2, 2, 4]
[2, 3, 1]
[2, 3, 2]
[2, 3, 3]
[2, 3, 4]
[2, 4, 1]
[2, 4, 2]
[2, 4, 3]
[2, 4, 4]
[3, 1, 1]
[3, 1, 2]
[3, 1, 3]
[3, 1, 4]
[3, 2, 1]
[3, 2, 2]
[3, 2, 3]
[3, 2, 4]
[3, 3, 1]
[3, 3, 2]
[3, 3, 3]
[3, 3, 4]
[3, 4, 1]
[3, 4, 2]
[3, 4, 3]
[3, 4, 4]
[4, 1, 1]
[4, 1, 2]
[4, 1, 3]
[4, 1, 4]
[4, 2, 1]
[4, 2, 2]
[4, 2, 3]
[4, 2, 4]
[4, 3, 1]
[4, 3, 2]
[4, 3, 3]
[4, 3, 4]
[4, 4, 1]
[4, 4, 2]
[4, 4, 3]
[4, 4, 4]
*******************
[1, 2, 3]
[1, 2, 4]
[1, 3, 2]
[1, 3, 4]
[1, 4, 2]
[1, 4, 3]
[2, 1, 3]
[2, 1, 4]
[2, 3, 1]
[2, 3, 4]
[2, 4, 1]
[2, 4, 3]
[3, 1, 2]
[3, 1, 4]
[3, 2, 1]
[3, 2, 4]
[3, 4, 1]
[3, 4, 2]
[4, 1, 2]
[4, 1, 3]
[4, 2, 1]
[4, 2, 3]
[4, 3, 1]
[4, 3, 2]
*******************
[1, 2, 3]
[1, 2, 4]
[1, 3, 4]
[2, 3, 4]