leetcode 216. Combination Sum III
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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.
Note:
- All numbers will be positive integers.
- The solution set must not contain duplicate combinations.
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]]
思路:回溯法
1 class Solution 2 public: 3 vector<vector<int>> combinationSum3(int k, int n) 4 if (k <= 0) 5 return ; 6 vector<vector<int> > res; 7 vector<int> v; 8 combinationSum3(k, n, res, v, 1); 9 return res; 10 11 private: 12 void combinationSum3(int k, int n, vector<vector<int> > &res, vector<int> &v, int begin) 13 if (int(v.size()) == k && n == 0) 14 res.push_back(v); 15 return ; 16 17 for (int i = begin; i <= 9 && n >= i; i++) 18 v.push_back(i); 19 combinationSum3(k, n - i, res, v, i + 1); 20 v.pop_back(); 21 22 23 ;
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