Update 0077.组合.md

problems/0077.组合.md

@@ -377,68 +377,42 @@ class Solution {
 ```
 
 ### Python
-
+未剪枝优化
 ```python
-class Solution(object):
+class Solution:
-    def combine(self, n, k):
+    def combine(self, n: int, k: int) -> List[List[int]]:
-        """
+        result = []  # 存放结果集
-        :type n: int
+        self.backtracking(n, k, 1, [], result)
-        :type k: int
+        return result
-        :rtype: List[List[int]]
+    def backtracking(self, n, k, startIndex, path, result):
-        """
-        result = []
-        path = []
-        def backtracking(n, k, startidx):
         if len(path) == k:
             result.append(path[:])
             return
+        for i in range(startIndex, n + 1):  # 需要优化的地方
+            path.append(i)  # 处理节点
+            self.backtracking(n, k, i + 1, path, result)
+            path.pop()  # 回溯，撤销处理的节点
 
-            # 剪枝， 最后k - len(path)个节点直接构造结果，无需递归
+```
-            last_startidx = n - (k - len(path)) + 1
 
-            for x in range(startidx, last_startidx + 1):
-                path.append(x)
-                backtracking(n, k, x + 1)  # 递归
-                path.pop()  # 回溯
 
-        backtracking(n, k, 1)
+剪枝优化：
+
+```python
+class Solution:
+    def combine(self, n: int, k: int) -> List[List[int]]:
+        result = []  # 存放结果集
+        self.backtracking(n, k, 1, [], result)
         return result
-```
+    def backtracking(self, n, k, startIndex, path, result):
-
-```python
-class Solution:
-    def combine(self, n: int, k: int) -> List[List[int]]:
-        res = []
-        path = []
-        def backtrack(n, k, StartIndex):
         if len(path) == k:
-                res.append(path[:])
+            result.append(path[:])
-                return
-            for i in range(StartIndex, n + 1):
-                path.append(i)
-                backtrack(n, k, i+1)
-                path.pop()
-        backtrack(n, k, 1)
-        return res
-```
-
-剪枝：
-
-```python
-class Solution:
-    def combine(self, n: int, k: int) -> List[List[int]]:
-        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 - (k - len(path)) + 2):  # 优化的地方
             path.append(i)  # 处理节点
-                backtrack(n,k,i+1)  #递归
+            self.backtracking(n, k, i + 1, path, result)
             path.pop()  # 回溯，撤销处理的节点
-        backtrack(n,k,1)
+
-        return res
 ```
 
 ### Go