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Author: Chris Wu

problems/swap-nodes-in-pairs.py

@@ -0,0 +1,57 @@
+class Solution(object):
+    def swapPairs(self, head):
+        pre_head = ListNode(-1)
+        curr = head
+        prev = pre_head
+
+        if not curr or not curr.next: return head
+
+        while curr and curr.next:
+            temp_next = curr.next.next
+
+            prev.next = curr.next
+            curr.next.next = curr
+            curr.next = temp_next
+
+            prev = curr
+            curr = temp_next
+
+        return pre_head.next
+
+
+from collections import deque
+class Solution(object):
+    def swapPairs(self, head):
+        curr = head
+        q1 = deque([])
+        q2 = deque([])
+        seq = 0
+        while curr:
+            if seq%2==0:
+                q2.append(curr)
+            else:
+                q1.append(curr)
+
+            temp = curr.next
+            curr.next = None #clear old link
+            curr = temp
+            seq+=1
+
+        if seq==1:
+            return head
+
+        use_q1 = True
+        pre_head = ListNode(-1)
+        curr = pre_head
+        while q1 or q2:
+            if use_q1:
+                if not q1: break
+                curr.next = q1.popleft()
+            else:
+                curr.next = q2.popleft()
+            curr = curr.next
+            use_q1 = not use_q1
+
+        if q2: curr.next = q2.popleft() #odd length of linked list
+
+        return pre_head.next