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class Solution {
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 public:
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  int specialArray(vector<int> &nums) {
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    int v[102];
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    memset(v, 0, sizeof v);
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    for (const auto &n : nums) {
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      ++v[n > 100 ? 100 : n];
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    }
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    for (int i = 100; i > 0; --i) {
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      v[i] = v[i + 1] + v[i];
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      if (v[i] == i) return i;
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    }
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    return -1;
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  }
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};