LeetCode Hot100. 124.二叉树中的最大路径和

class Solution {
public:
    int res = -INT_MAX;
    int dfs(TreeNode* root){
        if(!root) return 0;

        int left = dfs(root->left);//左子树的最大路径和
        int right = dfs(root->right);//右子树的最大路径和

        int innerMax = root->val + left + right;//当前子树内部最大和
        res = max(innerMax, res);
        int tempMax = max(left, right);
        int outterMax = root->val + max(0, tempMax);//子树给上级提供的最大和
        if(outterMax < 0) return 0;
        return outterMax;
    }
    int maxPathSum(TreeNode* root) {
        if(!root) return 0;
        dfs(root);
        return res;
    }
};