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class Solution {
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 public:
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  bool isValid(string s) {
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    stack<char> st;  // taking stack for keep tracking the order of the
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                     // brackets..
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    for (auto i : s) // iterate over each and every elements
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    {
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      if (i == '(' or i == '{' or i == '[')
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        st.push(i); // if current element of the string will be opening bracket
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                    // then we will just simply push it into the stack
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      else          // if control comes to else part, it means that current element is a
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                    // closing bracket, so check two conditions  current element matches
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                    // with top of the stack and the stack must not be empty...
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      {
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        if (st.empty() or (st.top() == '(' and i != ')') or (st.top() == '{' and i != '}') or
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            (st.top() == '[' and i != ']'))
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          return false;
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        st.pop(); // if control reaches to that line, it means we have got the
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                  // right pair of brackets, so just pop it.
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      }
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    }
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    return st.empty(); // at last, it may possible that we left something into the
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                       // stack unpair so return checking stack is empty or not..
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  }
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};