124. Binary Tree Maximum Path Sum

class Solution {
    
        int maxSum = Integer.MIN_VALUE;

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

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

        
        int leftMax = Math.max(dfs(node.left), 0); 
        int rightMax = Math.max(dfs(node.right), 0); 
       
        int currentPathSum = node.val + leftMax + rightMax;

        
        maxSum = Math.max(maxSum, currentPathSum);

      
        return node.val + Math.max(leftMax, rightMax);
    }
}