public class Leetcode124 {
    int res = Integer.MIN_VALUE;

    public int maxPathSum(TreeNode root) {
        dfs(root);
        return res;
    }

    public int dfs(TreeNode node) {
        if (node == null) return 0;

        // 递归计算左右节点的最大贡献值，如果为父，就不计算到以当前节点为根节点的最大路径中
        int leftNodeSum = Math.max(dfs(node.left),0);
        int rightNodeSum = Math.max(dfs(node.right),0);

        //更新答案
        int temp = node.val + leftNodeSum + rightNodeSum;
        res = Math.max(res, temp);

        return node.val + Math.max(leftNodeSum, rightNodeSum);
    }
}