BFS实现:

/**
 * 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 deepestLeavesSum(TreeNode* root) {
        queue<TreeNode *> queue;
        queue.push(root);
        int sum;
        
        while(!queue.empty())
        {
            sum = 0;
            int size = queue.size();
            for(int i = 0;i< size;i++)
            {
                TreeNode* curr = queue.front();
                queue.pop();
                sum += curr->val;
                if(curr->left) queue.push(curr->left);
                if(curr->right) queue.push(curr->right);
            }
        }
        
        return sum;
    }
};

DFS实现：

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

这道题目，BFS要比DFS更好理解和实现，使用DFS时要存储当前最大深度。如果遇到更大深度时清空sum。这里使用了类成员变量sum和max_depth，当成全局变量使用。