Number of Ways to Divide a Long Corridor LeetCode solution in C++

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class Solution {
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 public:
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  int numberOfWays(string corridor) {
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    // Store 1000000007 in a variable for convenience
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    const int MOD = 1e9 + 7;
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    // Initial values of three variables
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    int zero = 0;
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    int one = 0;
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    int two = 1;
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    // Compute using derived equations
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    for (char thing : corridor) {
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      if (thing == 'S') {
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        zero = one;
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        swap(one, two);
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      } else {
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        two = (two + zero) % MOD;
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      }
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    }
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    // Return the result
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    return zero;
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  }
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};