采用后序遍历
/**
* <p>给定一个二叉树，找出其最大深度。</p>
*
* <p>二叉树的深度为根节点到最远叶子节点的最长路径上的节点数。</p>
*
* <p><strong>说明:</strong> 叶子节点是指没有子节点的节点。</p>
*
* <p><strong>示例：</strong><br>
* 给定二叉树 <code>[3,9,20,null,null,15,7]</code>，</p>
*
* <pre> 3
* / \
* 9 20
* / \
* 15 7</pre>
*
* <p>返回它的最大深度 3 。</p>
* <div><div>Related Topics</div><div><li>树</li><li>深度优先搜索</li><li>广度优先搜索</li><li>二叉树</li></div></div><br><div><li>???? 1267</li><li>???? 0</li></div>
*/
//leetcode submit region begin(Prohibit modification and deletion)
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
int res = 0;
int depth = 0;
//解法2
public int maxDepth(TreeNode root) {
if(root==null){
res = Math.max(depth,res);
return res;
}
depth++;
maxDepth(root.left);
maxDepth(root.right);
depth--;
return res;
}
}
//leetcode submit region end(Prohibit modification and deletion)