LeetCode HOT100 - 二叉树的最大深度

就是直接搜索左右子树最大的长度让后向上传递即可

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode* root) {
        auto dfs = [&](this auto&& self, TreeNode* u) -> int {
            if (!u) {
                return 0;
            }
            return max(self(u->left), self(u->right)) + 1;
        };
        return dfs(root);
    }
};