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class Solution {
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  public int triangleNumber(int[] a) {
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    Arrays.sort(a);
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    int n = a.length;
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    int count = 0;
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    for (int i = n - 1; i >= 1; i--) {
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      int left = 0, right = i - 1;
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      while (left < right) {
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        if (a[left] + a[right] > a[i]) {
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          count += right - left;
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          right--;
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        } else left++;
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      }
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    }
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    return count;
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  }
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}