Given a binary tree, you need to compute the length of the diameter of the tree.

For example: Given binary tree

     5
   /  \
  3    20
       / \
      7   8
Return 3 as diameter [3,5,20,8] or [3,5,20,7]

Diameter of a node is the lheight+rheight. The problem can be solved with a similar approach involved in finding the height of the binary tree. Along with calculating the height maintain a variable to have the max diameter.

public class Solution { 
	int maxd = 0;
	public int diameterOfBinaryTree(TreeNode root) {
	    height(root);
		return maxd;
	}

	public int height(TreeNode root) {
		if (root == null)
			return 0;
		int lh = height(root.left);
		int rh = height(root.right);
		int d = lh + rh;
		if (d > maxd)
			maxd = d;
		return 1 + Math.max(lh, rh);
	}

	static class TreeNode {
		TreeNode left;
		TreeNode right;
		int val;

		public TreeNode(int value) {
			this.val = value;
		}
	}
}