题目:
Given two integersnandk, return all possible combinations ofknumbers out of 1 …n.
For example,Ifn= 4 andk= 2, a solution is:
[ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4],]题意:
给定两个整数 n 和 k,,返回1 …n中k个数字的所有的组合。
比方说,
如果n=4 and k=2,解为:
[ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4],]算法分析:
用一个循环递归处理子问题。
AC代码:
public class Solution {public ArrayList<ArrayList<Integer>> combine(int n, int k){ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();if(n<=0 || n<k)return res;helper(n,k,1,new ArrayList<Integer>(), res);return res;}private void helper(int n, int k, int start, ArrayList<Integer> item, ArrayList<ArrayList<Integer>> res){if(item.size()==k){res.add(new ArrayList<Integer>(item));return;}for(int i=start;i<=n;i++) // try each possibility number in current position{item.add(i);helper(n,k,i+1,item,res); // after selecting number for current position, process next positionitem.remove(item.size()-1); // clear the current position to try next possible number}}}
版权声明:本文为博主原创文章,转载注明出处
可是我知道结果是惨淡的,但还是心存希望!