title
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
排列组合问题
class Solution {
public:
void backtracking(vector<vector<int>>& res, vector<int> &t, int k, int n,int start) {
if (k == 0 && n == 0) {
res.push_back(t);
return;
}
if (k <= 0 || n <= 0 || start > 9) {
return;
}
for (int i = start; i <= 9; i++) {
t.push_back(i);
backtracking(res, t, k-1, n-i, i+1);
t.pop_back();
}
}
vector<vector<int>> combinationSum3(int k, int n) {
vector<vector<int>> res;
vector<int> t;
backtracking(res, t, k, n, 1);
return res;
}
};