package test;

import java.util.ArrayList;

import java.util.List;

/**

* Created by Administrator on 2018/3/28 0028.

*/

public class first {

List<List<Integer>> result=new ArrayList<List<Integer>>();

public List<List<Integer>> combine(int n, int k) {

List<Integer> list=new ArrayList<Integer>();

backtracking(n,k,1,list);

return result;

}

public void backtracking(int n,int k,int start,List<Integer>list){

if(k<0) return ;

else if(k==0){

result.add(new ArrayList(list));

}else{

for(int i=start;i<=n;i++){

list.add(i);

backtracking(n,k-1,i+1,list);

list.remove(list.size()-1);

}

}

}

public static void main(String[] args) {

first a=new first();

a.combine(4,3);

System.out.println(a.result);

}

}