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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]]
https://leetcode.com/problems/combination-sum-iii/
水题。另外该题还有一道扩展，如果只求给出方案的个数，不要求给出具体方案，而且数据量很大，那么就不能够用DFS了，这时候就得用动态规划来做，具体可以看我另一篇文章（k Sum）：
http://www.cnblogs.com/easonliu/p/4508185.html
1 class Solution { 2 public: 3 void dfs(int k, int n, int idx, int sum, int cnt, vector<int> &path, vector<vector<int> > &res) { 4 if (sum > n || cnt > k || idx > 10) return; 5 if (sum == n && cnt == k) { 6 res.push_back(path); 7 return; 8 } 9 dfs(k, n, idx + 1, sum, cnt, path, res); 10 path.push_back(idx); 11 dfs(k, n, idx + 1, sum + idx, cnt + 1, path, res); 12 path.pop_back(); 13 } 14 15 vector<vector<int>> combinationSum3(int k, int n) { 16 vector<vector<int>> res; 17 vector<int> path; 18 dfs(k, n, 1, 0, 0, path, res); 19 return res; 20 } 21 };
[LeetCode] Combination Sum III
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原文地址：http://www.cnblogs.com/easonliu/p/4525607.html
