Combination Sum III
Description
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]]
Solution
class Solution {
public:
vector<vector<int>> combinationSum3(int k, int n) {
vector<vector<int>> ans;
if(k > 10 || n > 45 || (1 + k) * k / 2 > n) return ans;
vector<int> nums;
dfs(1, k, n, nums, ans);
return ans;
}
void dfs(int min_num, int k, int n, vector<int> &nums, vector<vector<int>> &ans){
if(k == 0){
if(n == 0) ans.push_back(nums);
return;
}
for(int i = min_num; i <= min(9, n); ++i){
nums.push_back(i);
dfs(i + 1, k - 1, n - i, nums, ans);
nums.pop_back();
}
}
};
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