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class Solution {
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  public int specialArray(int[] nums) {
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    int x = nums.length;
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    int[] counts = new int[x + 1];
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    for (int elem : nums)
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      if (elem >= x) counts[x]++;
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      else counts[elem]++;
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    int res = 0;
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    for (int i = counts.length - 1; i > 0; i--) {
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      res += counts[i];
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      if (res == i) return i;
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    }
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    return -1;
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  }
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}