124. Binary Tree Maximum Path Sum

public class Solution{
	int maxValue;
	public int maxPathSum(TreeNode root){
		maxValue = Integer.MIN_VALUE;
		maxPathDown(root);
		return maxValue;
	}

	private int maxPathDown(TreeNode node){
		if(node == null){
			return 0;
		}
		int left = Math.max(0,maxPathDown(node.left));
		int right = Math.max(0, maxPathDown(node.right));
		maxValue = Math.max(maxValue, left + right + node.val);
		return Math.max(left, right) + node.val;
	}
}