标签：com out unique private == backtrack vat NPU positive
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:
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]]
Approach #1: BackTracking. [C++]
class Solution {
public:
vector<vector<int>> combinationSum3(int k, int n) {
vector<int> sol;
vector<vector<int>> ans;
helper(k, n, sol, ans);
return ans;
}
private:
void helper(const int k, int n, vector<int> v, vector<vector<int>>& ans) {
if (v.size() == k && n == 0) {
ans.push_back(v);
return;
}
if (v.size() < k) {
for (int i = v.empty()?1:v.back()+1; i <= 9; ++i) {
if (n - i < 0) break;
v.push_back(i);
helper(k, n-i, v, ans);
// this is I don‘t care in the first time.
v.pop_back();
}
}
}
};
标签：com out unique private == backtrack vat NPU positive
原文地址：https://www.cnblogs.com/ruruozhenhao/p/10347250.html
