题目：

题解：

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     struct TreeNode *left;*     struct TreeNode *right;* };*/
int max;
int dfs(struct TreeNode* root){if(!root) return 0;int left = dfs(root->left);int right = dfs(root->right);int l = fmax(root->val, root->val + left);int r = fmax(root->val, root->val + right);max = fmax(max, fmax(l + r - root->val, fmax(l, r)));return fmax(l, r);
}int maxPathSum(struct TreeNode* root){max = INT_MIN;dfs(root);return max;
}