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.

题目

给定一个二叉树，找出其最大深度。

二叉树的深度为根节点到最远叶子节点的距离。

分析

最简单的求深度的代码

代码

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
    public int maxDepth(TreeNode root) {
        // write your code here
        if (root == null)  
        {  
            return 0;  
        }  
        int left = maxDepth(root.left);  
        int right = maxDepth(root.right);  
        return (left > right) ? left + 1 : right + 1;
    }
}

非递归的方法

使用有一个栈即可

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null)
        return 0;
    
    Deque<TreeNode> stack = new LinkedList<TreeNode>();
    
    stack.push(root);
    int count = 0;
    
    while (!stack.isEmpty()) {
        int size = stack.size();
        while (size-- > 0) {
            TreeNode cur = stack.pop();
            if (cur.left != null)
                stack.addLast(cur.left);
            if (cur.right != null)
                stack.addLast(cur.right);
        }
        count++;

    }
    return count;
    }
}