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class Solution {
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 public:
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  string makeLargestSpecial(string s) {
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    if (s.length() == 0) return ""; // return null string if size is zero
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    vector<string> ans; // list to store all current special substrings
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    int count = 0,
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        i = 0; // keep track of special substring starting index using "i" and
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               //"count" to keep the track of special substring is over or not
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    for (int j = 0; j < s.size(); j++) {
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      if (s[j] == '1')
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        count++;
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      else
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        count--;
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      if (count == 0) {
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        // call recursively using mid special substring
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        ans.push_back('1' + makeLargestSpecial(s.substr(i + 1, j - i - 1)) + '0');
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        i = j + 1;
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      }
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    }
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    // sort current substring stored list to fulfill the question demand
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    sort(ans.begin(), ans.end(), greater<string>());
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    string finalString = "";
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    for (i = 0; i < ans.size(); i++) {
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      finalString += ans[i];
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    }
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    return finalString;
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  }
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};