Update 0102.二叉树的层序遍历.md

problems/0102.二叉树的层序遍历.md

@@ -2381,21 +2381,41 @@ python代码：
 
 ```python
 # 层序遍历解法
+"""
+# Definition for a Node.
+class Node:
+    def __init__(self, val: int = 0, left: 'Node' = None, right: 'Node' = None, next: 'Node' = None):
+        self.val = val
+        self.left = left
+        self.right = right
+        self.next = next
+"""
+
 class Solution:
     def connect(self, root: 'Node') -> 'Node':
         if not root:
-            return None
+            return root
-        queue = [root]
+        
-        while queue:  # 遍历每一层
+        queue = collections.deque([root])
-            length = len(queue)
+        
-            tail = None # 每一层维护一个尾节点
+        while queue:
-            for i in range(length): # 遍历当前层
+            level_size = len(queue)
-                curnode = queue.pop(0)
+            prev = None
-                if tail:
+            
-                    tail.next = curnode # 让尾节点指向当前节点
+            for i in range(level_size):
-                tail = curnode # 让当前节点成为尾节点
+                node = queue.popleft()
-                if curnode.left : queue.append(curnode.left)
+                
-                if curnode.right: queue.append(curnode.right)
+                if prev:
+                    prev.next = node
+                
+                prev = node
+                
+                if node.left:
+                    queue.append(node.left)
+                
+                if node.right:
+                    queue.append(node.right)
+        
         return root
 
 ```