Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;
import java.util.ArrayList;

import java.util.List;

public class Main {

    public static List<List<Integer>> getIndexSublist(int numbers, int length) {
        List<List<Integer>> sublists = new ArrayList<>();

        if (length > numbers) {
            return null;
            //if length==numbers
        } else if (length == numbers) {
            ArrayList<Integer> temp = new ArrayList<Integer>();
            for (int i = 0; i < numbers; i++) {
                temp.add(i);
            }
            sublists.add(temp);
            return sublists;
            //if length==1
        } else if (length == 1) {

            for (int i = 0; i < numbers; i++) {
                ArrayList<Integer> temp = new ArrayList<Integer>();
                temp.add(i);
                sublists.add(temp);
            }

            return sublists;
        }

        //for normal cases, initialize a list with one element
        for (int i = 0; i < numbers - length + 1; i++) {
            ArrayList<Integer> temp = new ArrayList<Integer>();
            temp.add(i);
            sublists.add(temp);
        }

        //recursively add more elements
        try {
            getIndexSublist(numbers, length, sublists);
        } catch (IndexOutOfBoundsException e) {
            return new ArrayList<>();
        }

        return sublists;
    }

    private static void getIndexSublist(int numbers, int length, List<List<Integer>> result) {

        List<List<Integer>> results = new ArrayList<>();
        results.addAll(result);

        if (result.get(0).size() == length) {
            return;
        }

        result.clear();
        for (List<Integer> one : results) {

            for (int i = 1; i < numbers; i++) {
                if (i > one.get(one.size() - 1)) {
                    ArrayList<Integer> temp = new ArrayList<Integer>();
                    temp.addAll(one);
                    temp.add(i);
                    result.add(temp);
                }
            }
        }
        getIndexSublist(numbers, length, result);
    }
}