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class Solution {
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 public:
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  bool judgeSquareSum(int c) {
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    long long start = 0, end = 0;
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    while (end * end < c) {
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      end++;
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    }
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    long long target = c;
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    while (start <= end) {
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      long long product = start * start + end * end;
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      if (product == target) {
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        return true;
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      } else if (product > c) {
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        end--;
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      } else {
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        start++;
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      }
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    }
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    return false;
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  }
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};