LeetCode(124) Binary Tree Maximum Path Sum

题目

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.

分析

给定一颗二叉树,求其最大路径和。对于二叉树,算法大多可以选择递归解决,此题也不例外。
如果只是一个节点,那么当然就是这个节点的值了.

如果这个作为root,那么最长路应该就是..

F(left) + F(right) + val...当然如果left,或者right<0就不用加了的= =

从下往上递归遍历...

如果不这个不是root,那么就不能把left和right加起来了...因为只是一条路...

AC代码

 /**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/ class Solution {
public:
int maxVal = INT_MIN;
int maxPathSum(TreeNode* root) {
if (root == NULL)
return ; maxSum(root);
return maxVal;
} /*递归函数*/
int maxSum(TreeNode *root)
{
if (root == NULL)
return ; /*求以root为根的当前子树的最大路径和*/
int curVal = root->val;
int lmaxSum = maxSum(root->left), rmaxSum = maxSum(root->right);
if (lmaxSum > )
curVal += lmaxSum;
if (rmaxSum > )
curVal += rmaxSum; if (curVal > maxVal)
maxVal = curVal; /*返回以当前root为根的子树的最大路径和*/
return max(root->val, max(root->val + lmaxSum, root->val + rmaxSum));
}
};
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