reversePolishNotation.cpp

/**
 * 
 * Reverse Polish Notation (RPN) is a mathematical notation where every operator follows all of its operands. For instance, to add three and four, one would write "3 4 +" rather than "3 + 4". If there are multiple operations, the operator is given immediately after its second operand; so the expression written "3 − 4 + 5" would be written "3 4 − 5 +" first subtract 4 from 3, then add 5 to that.
 * 
 * Transform the algebraic expression with brackets into RPN form.
 * 
 * You can assume that for the test cases below only single letters will be used, brackets [] will not be used and each expression has only one RPN form (no expressions like a*b*c)
 *
 * Input:
 * 
 * The first line contains t, the number of test cases (less then 100).
 * 
 * Followed by t lines, containing an expression to be translated to RPN form, where the length of the expression is less then 400.
 * 
 * Output:
 * 
 * The expressions in RPN form, one per line.
 * 
*/

#include <iostream>
#include <string>
#include <stack>
using namespace std;

int main()
{
  int t;
  cin >> t;
  cin.ignore();
  while (t--)
  {
    string exp = "", pexp = "";
    getline(cin, exp);
    stack<char> stack;

    for (auto &&i : exp)
    {
      switch (i)
      {
      case '(':
      case '+':
      case '-':
      case '/':
      case '*':
      case '^':
        stack.push(i);
        break;

      case ')':
        while (stack.top() != '(')
        {
          pexp += stack.top();
          stack.pop();
        }
        stack.pop();
        break;

      default:
        pexp += i;
        break;
      }
      // if(i == '(' || i >= '0' && i <= '9')
      // else if(i == ')')
      // {
      //   }
      // }
    }
    cout << pexp << "\n";
  }
  return 0;
}