题解 | #二叉树的最大深度#

/*
 * 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
        
        //return getMaxHeight(root);
        return maxHeight(root);
    }
    private int getMaxHeight(TreeNode root){
        if(root == null){
            return 0;
        }
      
        int left = getMaxHeight(root.left) +1;
        int right = getMaxHeight(root.right) +1;
        return Math.max(left, right);
    }
    private int maxHeight(TreeNode root){
        if(root == null){
            return 0;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        int res = 0;
        queue.add(root);
        while(!queue.isEmpty()){
            int size = queue.size();
            //遍历当前层的节点
            for(int i = 0;i<size;i++){
                TreeNode node = queue.poll();
                if(node.left != null){
                    queue.add(node.left);
                }
                if(node.right != null ){
                    queue.add(node.right);
                }
            }
            res ++;
            
            
        }
        return res;
    }
}