CODE 29. Maximum Depth of Binary Tree

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Given a binary tree, find its maximum depth.
The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

public int maxDepth(TreeNode root) {
	// Start typing your Java solution below
	// DO NOT write main() function
	if (null == root) {
		return 0;
	}
	Queue<TreeNode> queue = new LinkedList<TreeNode>();
	queue.offer(root);
	int layer = 1;
	int layerNumbers = 1;
	while (!queue.isEmpty()) {
		TreeNode node = queue.poll();
		layerNumbers--;

		if (null != node.left) {
			queue.offer(node.left);
		}
		if (null != node.right) {
			queue.offer(node.right);
		}
		if (layerNumbers == 0 && !queue.isEmpty()) {
			layerNumbers = queue.size();
			layer++;
		}
	}
	return layer;
}