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// ��������Please upvote if it helps ��������
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class Solution {
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 public:
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  string removeKdigits(string num, int k) {
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    // number of operation greater than length we return an empty string
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    if (num.length() <= k) return "0";
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    // k is 0 , no need of removing /  preforming any operation
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    if (k == 0) return num;
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    string res = ""; // result string
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    stack<char> s;   // char stack
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    s.push(num[0]); // pushing first character into stack
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    for (int i = 1; i < num.length(); ++i) {
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      while (k > 0 && !s.empty() && num[i] < s.top()) {
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        // if k greater than 0 and our stack is not empty and the upcoming
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        // digit, is less than the current top than we will pop the stack top
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        --k;
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        s.pop();
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      }
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      s.push(num[i]);
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      // popping preceding zeroes
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      if (s.size() == 1 && num[i] == '0') s.pop();
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    }
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    while (k && !s.empty()) {
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      // for cases like "456" where every num[i] > num.top()
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      --k;
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      s.pop();
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    }
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    while (!s.empty()) {
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      res.push_back(s.top()); // pushing stack top to string
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      s.pop();                // pop the top element
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    }
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    reverse(res.begin(), res.end()); // reverse the string
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    if (res.length() == 0) return "0";
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    return res;
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  }
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};