leetcode-124. Binary Tree Maximum Path Sum 二叉树中的最大路径和

Given a non-empty 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 must contain at least one node and does not need to go through the root. Example 1: Input: [1,2,3] 1 / \ 2 3 Output: 6 Example 2: Input: [-10,9,20,null,null,15,7]   -10    / \   9  20     /  \    15   7 Output: 42

给定一个非空二叉树，返回其最大路径和。 本题中，路径被定义为一条从树中任意节点出发，达到任意节点的序列。该路径至少包含一个节点，且不一定经过根节点。 示例 1: 输入: [1,2,3] 1 / \ 2 3 输出: 6 示例 2: 输入: [-10,9,20,null,null,15,7]   -10    / \   9  20     /  \    15   7 输出: 42

思路：参考http://www.cnblogs.com/grandyang/p/4280120.html

/**
 * 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 maxPathSum(TreeNode* root) {
        int res=INT_MIN;
        trival(root,res);
        return res;
    }
    int trival(TreeNode* root,int &res)
    {
        if(!root) return 0;
        int left = max(trival(root->left,res),0); //获取左子树最大值，小于0不取
        int right= max(trival(root->right,res),0);  
        res = max(res,left+right+root->val);   //res为遍历的所有结果的最大值
        return root->val + max(left,right);   //返回值定义为以当前节点为终点的path之和
    }
};