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class Solution {
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 public:
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  int ans = 0;
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  void dfs(TreeNode *root, string s) {
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    if (!root->left && !root->right) {
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      s += to_string(root->val);
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      ans += stoi(s);
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      return;
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    }
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    string o = s;
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    s += to_string(root->val);
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    if (root->left) dfs(root->left, s);
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    if (root->right) dfs(root->right, s);
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    s = o;
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  }
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  int sumNumbers(TreeNode *root) {
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    if (!root) return ans;
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    string s = "";
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    dfs(root, s);
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    return ans;
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  }
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};