Number of Substrings With Only 1s LeetCode solution in C++

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class Solution {
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  /*
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  To calculate the substring the formula is (n*n+1)/2 so just find the range and
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  calculate the substrings.
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  */
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  int mod = 1e9 + 7;
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  long calculateNumbeOfSubstrings(string &s, int &l, int &r) {
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    long range = r - l;
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    long ans = range * (range + 1) / 2;
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    return ans;
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  }
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 public:
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  int numSub(string s) {
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    int ans = 0;
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    int len = s.size();
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    int r = 0, l = 0;
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    while (r < len) {
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      while (r < len && s[l] != '1') {
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        l++;
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        r++;
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      }
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      while (r < len && s[r] != '0') {
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        r++;
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      }
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      ans = (ans + calculateNumbeOfSubstrings(s, l, r)) % mod;
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      l = r;
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    }
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    return ans;
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  }
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};