Merge pull request #237 from jojoo15/patch-20

修改 0077.组合 python3版本

Author: youngyangyang04

problems/0077.组合.md

@@ -370,23 +370,21 @@ class Solution {
 
 
 Python：
-```python
+```python3
 class Solution:
-    result: List[List[int]] = []
-    path: List[int] = []
     def combine(self, n: int, k: int) -> List[List[int]]:
-      self.result = []
-      self.combineHelper(n, k, 1)
-      return self.result
-
-    def combineHelper(self, n: int, k: int, startIndex: int):
-      if  (l := len(self.path)) == k:
-        self.result.append(self.path.copy())
-        return
-      for i in range(startIndex, n - (k - l) + 2):
-        self.path.append(i)
-        self.combineHelper(n, k, i + 1)
-        self.path.pop()
+        res=[]  #存放符合条件结果的集合
+        path=[]  #用来存放符合条件结果
+        def backtrack(n,k,startIndex):
+            if len(path) == k:
+                res.append(path[:])
+                return 
+            for i in range(startIndex,n+1):
+                path.append(i)  #处理节点 
+                backtrack(n,k,i+1)  #递归
+                path.pop()  #回溯，撤销处理的节点
+        backtrack(n,k,1)
+        return res
 ```
 javascript
 ```javascript