LeetCode 124. 二叉树中的最大路径和

/**
 * 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 ans;
    int dfs(TreeNode* root){
        if(!root)return 0;
        int left=max(0,dfs(root->left));
        int right=max(0,dfs(root->right));
        ans=max(ans,root->val+left+right);
        return root->val+max(left,right);
    }
    int maxPathSum(TreeNode* root) {
        ans=INT_MIN;
        dfs(root);
        return ans;
    }
};