添加0143重排链表 Python版本

problems/0143.重排链表.md

@@ -222,7 +222,61 @@ public class ReorderList {
 ```
 
 Python：
+```python3
+# 方法二 双向队列
+class Solution:
+    def reorderList(self, head: ListNode) -> None:
+        """
+        Do not return anything, modify head in-place instead.
+        """
+        d = collections.deque()
+        tmp = head
+        while tmp.next: # 链表除了首元素全部加入双向队列
+            d.append(tmp.next)
+            tmp = tmp.next
+        tmp = head
+        while len(d): # 一后一前加入链表
+            tmp.next = d.pop()
+            tmp = tmp.next
+            if len(d):
+                tmp.next = d.popleft()
+                tmp = tmp.next
+        tmp.next = None # 尾部置空
+ 
+# 方法三 反转链表
+class Solution:
+    def reorderList(self, head: ListNode) -> None:
+        if head == None or head.next == None:
+            return True
+        slow, fast = head, head
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+        right = slow.next # 分割右半边
+        slow.next = None # 切断
+        right = self.reverseList(right) #反转右半边
+        left = head
+        # 左半边一定比右半边长, 因此判断右半边即可
+        while right:
+            curLeft = left.next
+            left.next = right
+            left = curLeft
 
+            curRight = right.next
+            right.next = left
+            right = curRight
+
+
+    def reverseList(self, head: ListNode) -> ListNode:
+        cur = head   
+        pre = None
+        while(cur!=None):
+            temp = cur.next # 保存一下cur的下一个节点
+            cur.next = pre # 反转
+            pre = cur
+            cur = temp
+        return pre
+```
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