组合算法

package org.example.permandcombine;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

/**
 * @author xianzhe.ma
 * @date 2021/12/31
 */

public class Combination {

    public static void main(String[] args) {
        List<Integer> input = new ArrayList<>();
        input.add(1);
        input.add(2);
        input.add(3);
        input.add(4);
        combine(input,0,3,new LinkedList<>());

        for (ArrayList list : result) {
            System.out.println(list.toString());
        }
    }

    private static ArrayList<ArrayList<Integer>> result = new ArrayList<>();

    public static void combine(List<Integer> input, int start, int length, LinkedList<Integer> tempList) {
        if (length == 0) {
            ArrayList<Integer> list = new ArrayList<>();
            for (Integer num : tempList) {
                list.add(num);
            }
            result.add(list);
            return;
        }
        if (start == input.size()) {
            return;
        }

        tempList.add(input.get(start));
        combine(input,start+1,length - 1,tempList);
        tempList.removeLast();
        combine(input,start+1,length,tempList);
    }

}