insettion-sort-list

Author: Chris Wu

problems/insertion-sort-list.py

@@ -0,0 +1,41 @@
+# Definition for singly-linked list.
+class ListNode(object):
+    def __init__(self, x):
+        self.val = x
+        self.next = None
+
+
+class Solution(object):
+    def insertionSortList(self, node):
+        """
+        `pre_head` is a common technique that used in linked list problem.
+        So we don't need to handle the edge case all the time.
+        """
+        pre_head = ListNode(float('-inf'))
+        pre_head.next = node
+        pre = pre_head
+        while node:
+            if node.val>=pre.val: #see if node need to shift, if true, no need to shift this node
+                pre = node
+                node = node.next
+            else:
+                next_node = node.next
+                self.remove(pre, node)
+                self.insert(pre_head, node)
+                node = next_node
+        return pre_head.next
+
+    def remove(self, pre, node):
+        pre.next = node.next
+
+    def insert(self, pre_head, node):
+        curr = pre_head.next
+        pre = pre_head
+        while curr:
+            if node.val<curr.val:
+                pre.next = node
+                node.next = curr
+                break
+            pre = curr
+            curr = curr.next
+