07. Balanced Parenthesis(BRACKETS)

#include <iostream>
#include <climits>
#include <stack>
#include <string>
#include <vector>
#include <sstream>
using namespace std;

bool correctExpression(const string & expression)
{
  stack<char> brackets;

  for(int idx = 0; idx < expression.size(); idx++)
    {
      char curChar = expression[idx];

      char opening = 0;

      switch(curChar)
        {
          case '(':
          case '[':
          case '{':
          brackets.push(curChar);
          break;

          case ')':opening = '('; break;
          case ']':opening = '['; break;
          case '}':opening = '{'; break;
        }
      if(opening)
      {
        if(!brackets.size())
          return false; //incorrect expression
        if(brackets.top() != opening)
          return false;
        brackets.pop();
      }
    }
  return brackets.size() == 0;
}

int main()
{
  string buffer;
  cin >> buffer;

  cout << ( correctExpression(buffer) ? "YES" : "NO") << endl;
  return 0;
}