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class Solution {
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 public:
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  int findSecondMinimumValue(TreeNode *root) {
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    queue<TreeNode *> q;
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    q.push(root);
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    vector<int> v;
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    while (!q.empty()) {
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      v.push_back(q.front()->val);
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      if (q.front()->left) {
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        q.push(q.front()->left);
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      }
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      if (q.front()->right) {
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        q.push(q.front()->right);
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      }
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      q.pop();
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    }
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    sort(v.begin(), v.end());
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    int ans = -1;
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    for (int i = 1; i < v.size(); i++) {
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      if (v[i] != v[0]) {
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        return v[i];
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      }
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    }
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    return ans;
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  }
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};