LeetCode Maximum Depth of Binary Tree题目分析代码

/**
 * 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;
    }
}

/**
 * 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;
    }
}