Binary Tree Maximum Path Sum (pyemma)

public class BinaryTreeMaximumPathSum {
	public static int ma = Integer.MIN_VALUE;

	public static int maxPathSum(TreeNode root) {
		if(root == null) return 0;
		maxPath(root);
		return ma;
	}

	public static int maxPath(TreeNode root) {
		if(root.left == null && root.right == null) {
			ma = Math.max(ma, root.val);
			return root.val;
		}
		else if(root.left != null && root.right == null) {
			int left = maxPath(root.left);
			int better = Math.max(root.val, root.val+left);
			ma = Math.max(ma, better);
			return better;
		}
		else if(root.left == null && root.right != null) {
			int right = maxPath(root.right);
			int better = Math.max(root.val, root.val+right);
			ma = Math.max(ma, better);
			return better;
		}
		else {
			int left = maxPath(root.left);
			int right = maxPath(root.right);
			if(left >= 0 && right >= 0) {
				ma = Math.max(ma, root.val+left+right);
			}
			int better = Math.max(root.val, root.val+left);
			better = Math.max(better, root.val+right);
			ma = Math.max(ma, better);
			return better;
		}
	}
}