Binary Tree Maximum Path Sum

Author: gavinfish

124 Binary Tree Maximum Path Sum.py

@@ -0,0 +1,41 @@
+'''
+Given a binary tree, find the maximum path sum.
+
+For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path does not need to go through the root.
+
+For example:
+Given the below binary tree,
+
+       1
+      / \
+     2   3
+Return 6.
+'''
+
+# Definition for a binary tree node.
+class TreeNode(object):
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+
+
+class Solution(object):
+    def maxPathSum(self, root):
+        """
+        :type root: TreeNode
+        :rtype: int
+        """
+        self.maxSum = float('-inf')
+        self._maxPathSum(root)
+        return self.maxSum
+
+    def _maxPathSum(self, root):
+        if root is None:
+            return 0
+        left = self._maxPathSum(root.left)
+        right = self._maxPathSum(root.right)
+        left = left if left > 0 else 0
+        right = right if right > 0 else 0
+        self.maxSum = max(self.maxSum, root.val + left + right)
+        return max(left, right) + root.val