Number of Unique Good Subsequences LeetCode solution in C++

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class Solution {
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  int MOD = 1000000007;
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 public:
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  int numberOfUniqueGoodSubsequences(string binary) {
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    int zero = 0;
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    long long ones = 0;
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    long long zeros = 0;
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    for (int i = binary.size() - 1; i >= 0; --i) {
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      if (binary[i] == '1') {
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        ones = (ones + zeros + 1) % MOD;
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      } else {
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        zero = 1;
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        zeros = (ones + zeros + 1) % MOD;
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      }
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    }
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    return (ones + zero) % MOD;
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  }
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};