[LeetCode]题解（python）：124-Binary Tree Maximum Path Sum

[b]题目来源：[/b]

　　https://leetcode.com/problems/binary-tree-maximum-path-sum/

[b]题意分析：[/b]

　　给定一棵树，找出一个数值最大的路径，起点可以是任意节点或者叶子。

[b]题目思路：[/b]

　　我们可以先找路径的最大mr,ml，那么最大值是max（solve(root),solve(left),solve(right), max(mr + root.val + ml, root.val))。

[b]代码（python）：[/b]

　　

# 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
"""
def solve(root):
if root == None:
return 0
l,r = 0,0
if root.left:
l = max(solve(root.left),0)
if root.right:
r = max(solve(root.right),0)

ans1 = max(l,r) + root.val
ans2 = l + r + root.val
Solution.maxsum = max(Solution.maxsum,max(ans1,ans2))
print(Solution.maxsum)
return Solution.maxsum
if root == None:
return 0
Solution.maxsum = root.val
solve(root)
return Solution.maxsum

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