LeetCode 124. Binary Tree Maximum Path Sum

题目

思路

递归遍历，找到左子树和右子树最大的路径，返回加上当前节点的最大路径即可。

代码

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def __init__(self):
        self.maxNum = -99999
    def pathSum(self, root):
        if not root.left and not root.right:
            self.maxNum = max(self.maxNum, root.val)
            return root.val
        leftNum = 0; rightNum = 0
        if root.left: leftNum = self.pathSum(root.left)
        if root.right: rightNum = self.pathSum(root.right)
        self.maxNum = max(self.maxNum, root.val, root.val + leftNum, root.val + rightNum, root.val + leftNum + rightNum)
        return max(root.val, root.val + leftNum, root.val + rightNum)        
    def maxPathSum(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        self.pathSum(root)
        return self.maxNum