Combination Sum III

Desicription

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:
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Input: k = 3, n = 7
Output: [[1,2,4]]

Example 2:

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Input: k = 3, n = 9
Output: [[1,2,6], [1,3,5], [2,3,4]]

Solution

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class Solution {
private:
vector<vector<int>> res;
void dfs(vector<int>& current_vector, int current_sum, int current_number, const int k, const int n) {
for(int i = current_number + 1; i <= 9; i++) {
if(current_vector.size() == k - 1 && current_sum + i == n) {
current_vector.push_back(i);
res.push_back(current_vector);
current_vector.pop_back();
return ;
}
else if(current_vector.size() < k - 1 && current_sum + i < n) {
current_vector.push_back(i);
dfs(current_vector, current_sum + i, i, k, n);
current_vector.pop_back();
}
}
}
public:
vector<vector<int>> combinationSum3(int k, int n) {
vector<int> tmp{};
dfs(tmp, 0, 0, k, n);
return res;
}
};