add trees solutions

Author: hanksudo

102-binary-tree-level-order-traversal.py

@@ -0,0 +1,29 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution:
+    def levelOrder(self, root: TreeNode) -> List[List[int]]:
+        if root is None:
+            return []
+
+        vals = []
+        level = 0
+        queue = [(root, level)]
+        while queue:
+            # dequeue
+            node, level = queue.pop(0)
+            if len(vals) < level + 1:
+                vals.append([node.val])
+            else:
+                vals[level].append(node.val)
+
+            # enqueue
+            if node.left:
+                queue.append((node.left, level + 1))
+            if node.right:
+                queue.append((node.right, level + 1))
+        return vals

449-serialize-and-deserialize-bst.py

@@ -0,0 +1,63 @@
+# Definition for a binary tree node.
+class TreeNode:
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+
+from math import inf
+class Codec:
+
+    def serialize(self, root: TreeNode) -> str:
+        """Encodes a tree to a single string.
+        """
+        vals = []
+        def pre_order(root):
+            if root is None:
+                return ""
+
+            vals.append(str(root.val))
+            pre_order(root.left)
+            pre_order(root.right)
+        pre_order(root)
+        return " ".join(vals)
+
+    def deserialize(self, data: str) -> TreeNode:
+        """Decodes your encoded data to tree.
+        """
+        if not data:
+            return None
+
+        queue = data.split(" ")
+
+        def helper(q, min_value, max_value):
+            if not q:
+                return
+
+            val = int(q[0])
+            if val < min_value or val > max_value:
+                return
+            q.pop(0)
+            root = TreeNode(val)
+            root.left = helper(q, min_value, val)
+            root.right = helper(q, val, max_value)
+            return root
+        return helper(queue, -inf, inf)
+
+def pre_order(root):
+    if root is None:
+        return None
+    print(root.val)
+    pre_order(root.left)
+    pre_order(root.right)
+
+if __name__ == "__main__":
+
+    root = TreeNode(2)
+    root.left = TreeNode(1)
+    root.right = TreeNode(3)
+
+    codec = Codec()
+    node = codec.deserialize(codec.serialize(root))
+
+    pre_order(node) # 2 1 3