Abbreviating the Product of a Range LeetCode solution in C++

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class Solution {
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 public:
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  string abbreviateProduct(int left, int right) {
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    // upper 12 digit of product
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    double upper = 1;
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    // lower 12 digit of product
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    long long lower = 1L;
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    // offset to make 12 digit in upper and lower
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    long long Offset = 1e12;
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    // offset to make 5 digit in upper and lower
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    long long cutOffset = 1e5;
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    // store log value of the product
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    double product = 0.0;
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    // count trailing zero in the product
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    int trailing = 0;
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    for (int i = left; i <= right; i++) {
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      // update log value of product
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      product += log10(i);
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      // multiple value with upper and lower 12 digit
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      upper *= i;
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      lower *= i;
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      // keep 12 digit in upper
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      while (upper >= Offset) upper /= 10;
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      // remove trailing zeroes
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      while (lower % 10 == 0) lower /= 10, trailing++;
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      // keep 12 digits in lower
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      lower %= Offset;
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    }
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    // count total digits in product except trailing zeroes
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    int digitLength = (int)product + 1 - trailing;
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    // keep 5 digit in upper and lower
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    while (upper >= cutOffset) upper /= 10;
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    lower %= cutOffset;
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    int upperInt = upper;
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    // take digit length digits from upper and lower when digit length <= 10
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    if (digitLength <= 10) {
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      // make all digit 0 to tackle missing MSB zeroes in lower
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      string result(digitLength, '0');
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      string upperStr = to_string(upperInt);
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      string lowerStr = to_string(lower);
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      for (int i = 0; i < upperStr.length() && digitLength > 0; i++, digitLength--)
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        result[i] = upperStr[i];
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      for (int k = 1; !lowerStr.empty() && digitLength > 0; digitLength--, k++) {
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        result[result.length() - k] = lowerStr.back();
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        lowerStr.pop_back();
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      }
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      return result + "e" + to_string(trailing);
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    } else {
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      // take upper and lower 5 digits
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      string result = to_string(lower);
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      return to_string(upperInt) + "..." + string(5 - result.size(), '0') + result + "e" +
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             to_string(trailing);
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    }
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  }
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};