LeetCode-in-Java
216. Combination Sum III
Medium
Find all valid combinations of k numbers that sum up to n such that the following conditions are true:
- Only numbers
1through9are used. - Each number is used at most once.
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.
Example 4:
Input: k = 3, n = 2
Output: []
Explanation: There are no valid combinations.
Example 5:
Input: k = 9, n = 45
Output: [[1,2,3,4,5,6,7,8,9]]
Explanation:
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45
There are no other valid combinations.
Constraints:
2 <= k <= 91 <= n <= 60
Solution
import java.util.ArrayList;
import java.util.List;
@SuppressWarnings("java:S5413")
public class Solution {
public List<List<Integer>> combinationSum3(int k, int n) {
List<List<Integer>> res = new ArrayList<>();
solve(k, n, new ArrayList<>(), res, 0, 1);
return res;
}
private void solve(
int k, int target, List<Integer> temp, List<List<Integer>> res, int sum, int start) {
if (sum == target && temp.size() == k) {
res.add(new ArrayList<>(temp));
return;
}
if (temp.size() >= k) {
return;
}
if (sum > target) {
return;
}
for (int i = start; i <= 9; i++) {
temp.add(i);
solve(k, target, temp, res, sum + i, i + 1);
temp.remove(temp.size() - 1);
}
}
}