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class Solution {
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 public:
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  string smallestSubsequence(string s, int k, char letter, int repetition) {
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    int count = 0, inStack = 0;
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    int n = s.size();
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    for (int i = 0; i < n; i++)
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      if (s[i] == letter) count++;
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    string res = "";
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    int i = 0;
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    while (i < n) {
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      if (res.empty())
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        res.push_back(s[i]);
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      else {
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        while (!res.empty() && res.back() > s[i] && n - i + res.size() > k) {
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          if (res.back() == letter && count + inStack - 1 >= repetition) {
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            res.pop_back();
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            inStack--;
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          } else if (res.back() == letter)
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            break;
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          else
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            res.pop_back();
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        }
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        if (s[i] == letter) {
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          inStack++;
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          count--;
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        }
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        res.push_back(s[i]);
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      }
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      i++;
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    }
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    string ret = "";
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    for (int i = 0; i < res.size(); i++) {
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      if (res[i] == letter && repetition > 0 && k > 0) {
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        repetition--;
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        ret += res[i];
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        k--;
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      } else if (k - repetition > 0) {
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        k--;
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        ret += res[i];
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      }
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    }
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    return ret;
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  }
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};
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/*
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if(find helpful) {
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do upvote(); // thanks
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}
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*/