二叉树的深度

【题目】输入一棵二叉树，求该树的深度。从根结点到叶结点依次经过的结点（含根、叶结点）形成树的一条路径，最长路径的长度为树的深度。

public class TreeDepth {
	public class TreeNode {
		int val = 0;
		TreeNode left = null;
		TreeNode right = null;

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

	public int TreeDepth(TreeNode head) {
		if (head == null) {
			return 0;
		}
		Queue<TreeNode> queue = new LinkedList<TreeNode>();
		int count = 0;
		int res = 0;
		int nextCount = 0;
		queue.offer(head);
		while (!queue.isEmpty()) {
			head = queue.poll();
			count++;
			if (head.left != null) {
				queue.offer(head.left);
			}
			if (head.right != null) {
				queue.offer(head.right);
			}
			if (count == nextCount) {
				nextCount = queue.size();
				count = 0;
				res++;
			}
		}
		return res;
	}
}