1302. 层数最深叶子节点的和

给你一棵二叉树的根节点 root ，请你返回 层数最深的叶子节点的和 。

示例 1：

输入：root = [1,2,3,4,5,null,6,7,null,null,null,null,8]
输出：15

示例 2：

输入：root = [6,7,8,2,7,1,3,9,null,1,4,null,null,null,5]
输出：19

提示：

树中节点数目在范围 [1, 104] 之间。
1 <= Node.val <= 100

/**
 * 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 {
private:
    int maxLevel = -1;
    int sum = 0;
public:
    int deepestLeavesSum(TreeNode* root) {
        dfs(root, 0);
        return sum;
    }
    void dfs(TreeNode *node, int level){
        if (node == nullptr) {
            return;
        }
        if (level > maxLevel) {
            maxLevel = level;
            sum = node->val;
        } else if (level == maxLevel) {
            sum += node->val;
        }
        dfs(node->left, level + 1);
        dfs(node->right, level + 1);
    }
};