LeetCode in Kotlin
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.
Constraints:
2 <= k <= 91 <= n <= 60
Solution
class Solution {
fun combinationSum3(k: Int, n: Int): List<List<Int>> {
val a = MutableList(0) { MutableList(0) { 0 } }
comb(a, k, n, 1, MutableList<Int>(0) { 0 })
return a
}
fun comb(a: MutableList<MutableList<Int>>, k: Int, n: Int, index: Int, tmp: MutableList<Int>) {
if (n < 0) {
return
}
if (tmp.size > k) {
return
}
if (n == 0 && tmp.size == k) {
a.add(tmp.map { it }.toMutableList())
return
}
for (i in index until 10) {
tmp.add(i)
comb(a, k, n - i, i + 1, tmp)
tmp.removeAt(tmp.size - 1)
}
}
}