Find all valid combinations of k numbers that sum up to n such that the following conditions are true:
1 through 9 are used.Return a list of all possible valid combinations. The list must not contain the same combination twice, and the combinations may be returned in any order.
Example 1:
Input: k = 3, n = 7 Output: [[1,2,4]] Explanation: 1 + 2 + 4 = 7 There are no other valid combinations.
Example 2:
Input: k = 3, n = 9 Output: [[1,2,6],[1,3,5],[2,3,4]] Explanation: 1 + 2 + 6 = 9 1 + 3 + 5 = 9 2 + 3 + 4 = 9 There are no other valid combinations.
Example 3:
Input: k = 4, n = 1 Output: [] Explanation: There are no valid combinations. Using 4 different numbers in the range [1,9], the smallest sum we can get is 1+2+3+4 = 10 and since 10 > 1, there are no valid combination.
Constraints:
2 <= k <= 91 <= n <= 60
class Solution {
public:
vector<vector<int>> ans;
void solve(int k, int target, vector<int> &x, int start)
{
if(k==0 and target==0)
{
ans.push_back(x);
return;
}
if(k==0 || target==0) return;
for(int i=start; i<=9; i++)
{
if(i<=target)
{
x.push_back(i);
solve(k-1,target-i,x,i+1);
x.pop_back();
}
}
}
vector<vector<int>> combinationSum3(int k, int n) {
vector<int> x;
solve(k,n,x,1);
return ans;
}
};
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