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Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers.
Ensure that numbers within the set are sorted in ascending order.
Example 1:
Input: k = 3, n = 7
Output:
[[1,2,4]]
Example 2:
Input: k = 3, n = 9
Output:
[[1,2,6], [1,3,5], [2,3,4]]
public class Solution { List<List<Integer>> res; List<Integer> seq; public List<List<Integer>> combinationSum3(int k, int n) { //dfs,for循环和递归叠加。 //需要保存level值，因为结果要求是递增的，同时为了确保是k个数，每一次递归，k要减一 res=new ArrayList<List<Integer>>(); seq=new ArrayList<Integer>(); dfs(k,n,1,0); return res; } public void dfs(int k,int n,int start,int sum){ if(sum==n&&k==0){ res.add(new ArrayList<Integer>(seq)); }else if(sum>n||k<=0) return; for(int i=start;i<=9;i++){ seq.add(i); dfs(k-1,n,i+1,sum+i); seq.remove(seq.size()-1); } } }
[leedcode 216] Combination Sum III
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原文地址：http://www.cnblogs.com/qiaomu/p/4709205.html
