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.
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.
Solution
class Solution:
def combine(self, n: int, k: int) -> List[List[int]]:
out = []
def backtrack(i, cur):
if len(cur) == k:
out.append(cur.copy())
return
for j in range(i, n):
cur.append(j+1)
backtrack(i + 1, cur)
cur.pop()
i += 1
backtrack(0, [])
return out