diameterofBinaryTree*

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Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.

Example:
Given a binary tree 
          1
         / \
        2   3
       / \     
      4   5    
Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

Note: The length of path between two nodes is represented by the number of edges between them.
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class Solution {
public:
	int diameterOfBinaryTree(TreeNode * root) {
		int res = 0;
		maxDepth(root, res);
		return res;
	}
	int maxDepth(TreeNode *node, int &res) {
		if (node == NULL) {
			return 0;
		}
		int left = maxDepth(node->left, res);
		int right = maxDepth(node->right, res);
		res = max(res, left + right);
		return max(left, right) + 1;
	}
};