Concatenation of Consecutive Binary Numbers LeetCode solution in C++

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class Solution {
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 public:
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  int numberOfBits(int n) {
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    return log2(n) + 1;
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  }
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  int concatenatedBinary(int n) {
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    long ans = 0, MOD = 1e9 + 7;
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    for (int i = 1; i <= n; ++i) {
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      int len = numberOfBits(i);
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      ans = ((ans << len) % MOD + i) % MOD;
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    }
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    return ans;
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  }
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};