Complement of Base 10 Integer LeetCode solution in C++

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class Solution {
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 public:
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  int bitwiseComplement(int num) {
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    // base case
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    if (num == 0) return 1;
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    unsigned mask = ~0;
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    while (mask & num) mask = mask << 1;
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    return ~num ^ mask;
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  }
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};