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combinations_77.py
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combinations_77.py
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# 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.
# Constraints:
# 1 <= n <= 20
# 1 <= k <= n
# ---------------------------------------Runtime 770 ms Beats 58.21% Memory 64.83 MB Beats 75.65%---------------------------------------
from typing import List
class Solution:
def combine(self, n: int, k: int) -> List[List[int]]:
result = []
def backtracking(arr: list[int], path: []):
if len(path) == k:
result.append(path[:])
if len(path) < k:
for i, v in enumerate(arr):
path.append(v)
backtracking(arr[i + 1 :], path)
path.pop()
backtracking(list(range(1, n + 1)), [])
return result