class Solution {
public:
    int dfs(TreeNode* root,int u){
        if(!root)return 0;
        u=u*10+root->val;
        if(!root->left&&!root->right) return u;
        return dfs(root->left,u)+dfs(root->right,u);
    }
    int sumNumbers(TreeNode* root) {
        return dfs(root,0);
    }
};