Maximum Binary String After Change LeetCode solution in C++

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class Solution {
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 public:
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  string maximumBinaryString(string binary) {
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    int n = binary.size();
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    int z_count = 0;  // count the number of zeros
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    int z_index = -1; // index of the leftmost zero that is why we start
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                      // iterating from the right
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    for (int i = n - 1; i >= 0; i--) {
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      if (binary[i] == '0') {
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        z_count++;
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        z_index = i;
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        binary[i] = '1'; // changing all occurances to 1
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      }
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    }
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    if (z_index != -1) // to check if there is atleast 1 zero
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    {
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      binary[z_index + z_count - 1] = '0'; // this is the only zero present
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      // -1 because the only zero is also included in zero count
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    }
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    return binary;
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  }
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};