题目：

题解：

class Solution {
public:
    int sumNumbers(TreeNode* root) {
        if (root == nullptr) {
            return 0;
        }
        int sum = 0;
        queue<TreeNode*> nodeQueue;
        queue<int> numQueue;
        nodeQueue.push(root);
        numQueue.push(root->val);
        while (!nodeQueue.empty()) {
            TreeNode* node = nodeQueue.front();
            int num = numQueue.front();
            nodeQueue.pop();
            numQueue.pop();
            TreeNode* left = node->left;
            TreeNode* right = node->right;
            if (left == nullptr && right == nullptr) {
                sum += num;
            } else {
                if (left != nullptr) {
                    nodeQueue.push(left);
                    numQueue.push(num * 10 + left->val);
                }
                if (right != nullptr) {
                    nodeQueue.push(right);
                    numQueue.push(num * 10 + right->val);
                }
            }
        }
        return sum;
    }
};