题解 | #二叉树的最大深度#基于层序遍历借助队列实现，代码多点，但是好理解效率不能算差

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param root TreeNode类 
     * @return int整型
     */
    public int maxDepth (TreeNode root) {
        // write code here
        //本质上还是层序遍历 比层序遍历更简单
        if(root == null){
            return 0;
        }
        int depth = 0;
        Queue<TreeNode> q = new LinkedList<>();
        q.offer(root);
        while(!q.isEmpty()){
            int size = q.size();
            for(int i = 0;i < size;i++){
                TreeNode node = q.poll();
                if(node.left != null){
                    q.offer(node.left);
                }
                if(node.right != null){
                    q.offer(node.right);
                }
            }
            depth += 1;
        }
        return depth;
    }
}