Update 77_Combinations.md

Author: koji

77_Combinations.md

@@ -31,26 +31,21 @@ Constraints:
 
 ```python
 def combine(self, n: int, k: int) -> List[List[int]]:
- def gen_pattern(nums, k):
-  if k == 0:
-  return [[]]
- if k == 1:
- return [[num] for num in nums]
+ result = []
+ def gen_pattern(build, index):
+ if len(build) ==k:
+  result.append(build)
+ return
 
- res = []
- for i in range(len(nums)):
- perms = gen_pattern(nums[i+1:], k-1)
- for p in perms:
- res.append([nums[i]] + p) 
- return res
- 
- nums = list(range(1, n+1))
- res = gen_pattern(nums, k)
- return res
+ for i in range(index+1, n+1):
+ gen_pattern(build+[i], i)
+ 
+ gen_pattern([], 0)
+ return result
 ```
 
 
 ```
-Runtime: 556 ms, faster than 37.57% of Python3 online submissions for Combinations.
-Memory Usage: 16.2 MB, less than 33.85% of Python3 online submissions for Combinations.
+Runtime: 544 ms, faster than 43.06% of Python3 online submissions for Combinations.
+Memory Usage: 15.6 MB, less than 33.85% of Python3 online submissions for Combinations.
 ```