Count Vowels Permutation LeetCode solution in C++

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class Solution {
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 public:
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  int countVowelPermutation(int n) {
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    long a = 1, e = 1, i = 1, o = 1, u = 1, mod = pow(10, 9) + 7;
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    long a2, e2, i2, o2, u2;
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    for (int j = 2; j <= n; j++) {
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      a2 = (e + i + u) % mod;
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      e2 = (a + i) % mod;
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      i2 = (e + o) % mod;
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      o2 = i;
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      u2 = (o + i) % mod;
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      a = a2, e = e2, i = i2, o = o2, u = u2;
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    }
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    return (a + e + i + o + u) % mod;
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  }
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};