二叉树最大深度

给定一个二叉树 root ，返回其最大深度。

二叉树的 最大深度 是指从根节点到最远叶子节点的最长路径上的节点数。

求最大深度的问题，最常用的是用递归+深度优先探索

如果我们知道了左子树和右子树的最大深度 l 和 r，那么该二叉树的最大深度即为max(l,r)+1

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
*/
int maxDepth(struct TreeNode* root) {
    if(root==NULL)return 0;
    return fmax(maxDepth(root->left),maxDepth(root->right))+1;
}

python的写法

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def maxDepth(self, root: Optional[TreeNode]) -> int:
        if root is None:
            return 0
        else:
            left_height=self.maxDepth(root.left)
            right_height=self.maxDepth(root.right)
            return max(left_height,right_height)+1

Java的写法

/**
 * 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 {
    public int maxDepth(TreeNode root) {
        if(root==null)
        return 0;
        else
        {
            int leftHeight=maxDepth(root.left);
            int rightHeight=maxDepth(root.right);
            return Math.max(leftHeight,rightHeight)+1;
        }
    }
}