解法一:递归
class Solution {
public int maxDepth(TreeNode root) {
if(root==null)
return 0;
return Math.max(maxDepth(root.left),maxDepth(root.right))+1;
}
}
解法二：层序遍历的思想
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int maxDepth(TreeNode root) {
if(root == null) return 0;
List<TreeNode> queue = new LinkedList<>();
queue.add(root);
int res = 0;
while(!queue.isEmpty()) {
List<TreeNode> tmp = new LinkedList<>();
for(TreeNode node : queue) {
if(node.left != null) tmp.add(node.left);
if(node.right != null) tmp.add(node.right);
}
queue = tmp;
res++;
}
return res;
}
}
层序遍历思路总结：
