fakecoder2
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diff --git a/‎leetcode/143. Reorder List.py
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+'''
+Given a singly linked list L: L0→L1→…→Ln-1→Ln,
+reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…
+
+You must do this in-place without altering the nodes' values.
+
+For example,
+Given {1,2,3,4}, reorder it to {1,4,2,3}.
+'''
+
+
+# Definition for singly-linked list.
+class ListNode(object):
+    def __init__(self, x):
+        self.val = x
+        self.next = None
+
+class Solution(object):
+    def reorderList(self, head):
+        if not head or not head.next:
+            return
+        ahead, behind = self.split(head)
+        behind = self.reverse(behind)
+        head = self.reConnect(ahead, behind)
+    # split the linkedlist in middle
+    def split(self, head):
+        fast = head
+        slow = head
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next
+            fast = fast.next
+        middle = slow.next
+        slow.next = None
+        return head, middle
+    # reverse the behind half linkedlist
+    def reverse(self, head):
+        reHead = None
+        curNode = head
+        while curNode:
+            nextNode = curNode.next
+            curNode.next = reHead
+            reHead = curNode
+            curNode = nextNode
+        return reHead
+    # merge the two linkedlist to one
+    def reConnect(self, first, second):
+        head = first
+        tail = first
+        first = first.next
+        while second:
+            tail.next = second
+            tail = tail.next
+            second = second.next
+            if first:
+                first, second = second, first
+        return head