pairs

Author: Yubin Bai

Diff for: common_questions/swap_in_pairs/main.py

@@ -0,0 +1,31 @@
+# Given a linked list, swap every two adjacent nodes and return its head.
+# For example,
+# Given 1->2->3->4, you should return the list as 2->1->4->3.
+# Your algorithm should use only constant space. You may not modify the
+# values in the list, only nodes itself can be changed
+
+def swapInPairs(head):
+    if head == None:
+        return None
+    if head.next == None:
+        return head
+    prev = head
+    curr = head.next
+    newHead = curr
+
+    while True:
+        nextPrev = curr.next
+        if nextPrev == None:  # reached end of list
+            curr.next = prev
+            prev.next = None
+            break
+        nextCurr = nextPrev.next
+        if nextCurr == None:
+            curr.next = prev
+            prev.next = nextPrev
+            break
+        curr.next = prev
+        prev.next = nextCurr
+        prev = nextPrev
+        curr = nextCurr
+    return newHead