leetcode Combinations

题目链接

思路：
递归回溯

public class Solution {
    int n;
    int k;
    //boolean record[];
    LinkedList<List<Integer>>result;
    LinkedList<Integer>temp;
    public List<List<Integer>> combine(int n, int k) {
        this.n=n;
        this.k=k;

        result=new LinkedList<List<Integer>>();
        temp=new LinkedList<Integer>();
        help(0,1);

        return result;
    }

    void help(int step,int starIndex)
    {
        if(step==k)
        {
            result.add(new LinkedList<Integer>(temp));
            return;
        }
        for(int i=starIndex;i<=n;i++)
        {
            temp.add(i);
            help(step+1,i+1);
            temp.removeLast();
        }
    }
}