Create maximum-difference-between-node-and-ancestor.py

Author: kamyu104

Python/maximum-difference-between-node-and-ancestor.py

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+# Time:  O(n)
+# Space: O(h)
+
+# Definition for a binary tree node.
+class TreeNode(object):
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+
+
+# iterative stack solution
+class Solution(object):
+    def maxAncestorDiff(self, root):
+        """
+        :type root: TreeNode
+        :rtype: int
+        """
+        result = 0
+        stack = [(root, 0, float("inf"))]
+        while len(stack) > 0:
+            node, mx, mn = stack.pop()
+            if not node:
+                continue
+            result = max(result, mx-node.val, node.val-mn)
+            mx = max(mx, node.val)
+            mn = min(mn, node.val)
+            stack.append((node.left, mx, mn))
+            stack.append((node.right, mx, mn))
+        return result
+
+
+# Time:  O(n)
+# Space: O(h)
+# recursive solution
+class Solution2(object):
+    def maxAncestorDiff(self, root):
+        """
+        :type root: TreeNode
+        :rtype: int
+        """
+        def maxAncestorDiffHelper(node, mx, mn): 
+            if not node:
+                return 0
+            result = max(mx-node.val, node.val-mn)
+            mx = max(mx, node.val)
+            mn = min(mn, node.val)
+            result = max(result, maxAncestorDiffHelper(node.left, mx, mn))
+            result = max(result, maxAncestorDiffHelper(node.right, mx, mn))
+            return result
+
+        return maxAncestorDiffHelper(root, 0, float("inf"))