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35 lines (33 loc) · 1012 Bytes
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package LeetCode;
import java.util.ArrayList;
import java.util.List;
public class Combinations {
private static List<List<Integer>> res=new ArrayList<>();
public static List<List<Integer>>combine(int n,int k){
helper(n,1,k,new ArrayList<>());
return res;
}
public static void helper(int n,int start,int k,List<Integer>sumList){
if (k==0){
res.add(new ArrayList<>(sumList));
}
//注意这里的长度:终点-起点+1
if(k<0||n-start+1<k){
return;
}
for(int i=start;i<n+1;i++){
sumList.add(i);
System.out.println("***"+sumList+"***");
helper(n,i+1,k-1,sumList);
System.out.println("---"+sumList+"---");
sumList.remove(sumList.size()-1);
}
}
public static void main(String[] args){
int n=4;
int k=2;
// combine(4,2);
List<List<Integer>> result=combine(4,3);
System.out.println(result);
}
}