124. Binary Tree Maximum Path Sum

Find the contiguous subarray within an array (containing at least one number) which has the largest product.

For example, given the array [2,3,-2,4],

the contiguous subarray [2,3] has the largest product = 6.

public int maxPathSum(TreeNode root) {
    int[] res = new int[1];
    res[0] = Integer.MIN_VALUE;
    return maxPath(root, res);
    
}
    private int maxPath(TreeNode root, int[] res) {
    if (root == null)
        return;
    int left = maxPath(root.left, res);//左边一支儿（不算自己）
    int right = maxPath(root.right, res);
    int arch = left + right + root.val; //穿过自己
    int single = Math.max(root.val, Math.max(left, right) + root.val);
    //（算上自己）
    res[0] = Math.max(res[0], Math.max(arch, single));//update结果
    return res[0];
}