Add Binary LeetCode solution in C++

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class Solution {
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 public:
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  string addBinary(string a, string b) {
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    string ans;
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    int i = a.length() - 1, j = b.length() - 1;
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    int carry = 0;
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    while (carry || i >= 0 || j >= 0) {
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      if (i >= 0) {
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        carry += a[i] - '0';
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        i--;
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      }
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      if (j >= 0) {
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        carry += b[j] - '0';
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        j--;
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      }
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      ans += carry % 2 + '0';
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      carry = carry / 2;
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    }
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    reverse(ans.begin(), ans.end());
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    return ans;
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  }
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};