Merge pull request #186 from Pulkit-100/main

Closes #128

Python/449_Serialize_and_Deserialize_BST.py

@@ -0,0 +1,93 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Codec:
+
+    def inord(self, root, arr):
+        if not root:
+            return
+        self.inord(root.left,arr)
+        arr.append(str(root.val))
+        self.inord(root.right,arr)
+
+    def postord(self, root, arr):
+        if not root:
+            return
+        self.postord(root.left,arr)
+        self.postord(root.right,arr)
+        arr.append(str(root.val))
+
+
+    def serialize(self, root: TreeNode) -> str:
+        """Encodes a tree to a single string.
+        """
+        inorder = []
+        postorder = []
+
+        self.inord(root, inorder)
+        self.postord(root, postorder)
+
+        string = ",".join(inorder) + '$' + ','.join(postorder)
+        print(string)
+        return string
+
+    def deserialize(self, data: str) -> TreeNode:
+        """Decodes your encoded data to tree.
+        """
+        if data == "$":
+            return None
+        inorder, postorder = data.split('$')
+        inorder = [int(i) for i in inorder.split(',')]
+        postorder = [int(i) for i in postorder.split(',')]
+
+        return self.buildTree(inorder,postorder) 
+
+
+    def buildTree(self, inorder: List[int], postorder: List[int]) -> TreeNode:
+        inorderDict = {}
+        n = len(inorder)
+        for i in range(n):
+            inorderDict[inorder[i]] = i
+
+        start = 0
+        end = n-1
+
+        self.head = None
+
+        self.build(inorder, postorder, inorderDict, None, start, end, False, n-1)
+
+        return self.head
+
+
+    def build(self, inorder, postorder, inorderDict, head, start, end, left, rootIndex ):
+        if start > end:
+            return rootIndex
+        nodeVal = postorder[rootIndex]
+        index = inorderDict[nodeVal]
+        rootIndex -= 1
+        if head == None:
+            head = TreeNode(nodeVal)
+            self.head = head
+        elif left:
+            head.left = TreeNode(nodeVal)
+            head = head.left
+        else:
+            head.right = TreeNode(nodeVal)
+            head = head.right
+
+        rootIndex = self.build(inorder, postorder, inorderDict, head, index+1, end, False, rootIndex)
+        rootIndex = self.build(inorder, postorder, inorderDict, head, start, index-1, True, rootIndex)
+
+        return rootIndex
+
+# Your Codec object will be instantiated and called as such:
+# Your Codec object will be instantiated and called as such:
+# ser = Codec()
+# deser = Codec()
+# tree = ser.serialize(root)
+# ans = deser.deserialize(tree)
+# return ans