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class Solution {
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  public boolean isPerfectSquare(int num) {
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    long start = 1;
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    long end = num;
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    while (start <= end) {
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      long mid = start + (end - start) / 2;
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      if (mid * mid == num) {
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        return true;
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      } else if (mid * mid < num) {
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        start = mid + 1;
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      } else end = mid - 1;
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    }
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    return false;
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  }
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}