Given two integers k and target, return all combinations of EXACTLY k DISTINCT numbers chosen from the set {1, 2, 3, ..., 9} whose sum equals target. Each number may appear at most once in each combination. The output must be:
1. Each combination in strictly increasing order.
2. The list of combinations sorted lexicographically.
Return an empty list if no such combination exists.
Input: Two integers k and target separated by a comma.
Output: Canonically sorted list of k-element combinations.
Input: 3, 7
Output: [[1,2,4]]
Explanation: Only 1+2+4 = 7 with 3 distinct digits in [1..9].Input: 3, 9
Output: [[1,2,6],[1,3,5],[2,3,4]]
Explanation: Three combinations summing to 9.Input: 4, 1
Output: []
Explanation: No 4 distinct [1..9] digits sum to 1.1 <= k <= 91 <= target <= 60