Given two integers n and k, return all possible combinations of k numbers chosen from the range [1, n].
You may return the answer in any order.
Examples
Example 1
Input: n = 4, k = 2
Output: [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
Explanation: There are 4 choose 2 = 6 total combinations.
Note that combinations are unordered, i.e., [1,2] and [2,1] are considered to be the same combination.
Example 2
Input: n = 1, k = 1
Output: [[1]]
Explanation: There is 1 choose 1 = 1 total combination.
Constraints
1 <= n <= 20
1 <= k <= n
77. Combinations
Medium
30 Points
Backtracking
Given two integers n and k, return all possible combinations of k numbers chosen from the range [1, n].
You may return the answer in any order.
Examples
Example 1
Input: n = 4, k = 2
Output: [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
Explanation: There are 4 choose 2 = 6 total combinations.
Note that combinations are unordered, i.e., [1,2] and [2,1] are considered to be the same combination.
Example 2
Input: n = 1, k = 1
Output: [[1]]
Explanation: There is 1 choose 1 = 1 total combination.