reversed_poland.cc

#include<vector>
#include<iostream>
#include<string>
#include<math.h>
#include<stdlib.h>

template<typename T>
class Stack {
  int cur;
  std::vector<T> array;
public:
  Stack() {
    cur = 0;
    array = std::vector<T>(256);
  }
  void push(T v) {
    cur++;
    array[cur-1] =  v;
  }
  T pop() {
    T ret = array[cur-1];
    cur--;
    return ret;
  }
};



int eval(std::vector<std::string>& v) {
  Stack<int> stack;
  
  for (int i=0;i<v.size();i++) {
    std::string c = v[i];
  
    if(c.compare("+")==0) {
      int a = stack.pop();
      int b = stack.pop();
      //printf("%d + %d \n",b,a);
      stack.push(a + b) ;
    }
    else if(c.compare("-")==0) {
      int a = stack.pop();
      int b = stack.pop();
      //printf("%d - %d \n",a,b);
      stack.push(b - a) ;
    }
    else if(c.compare("*")==0) {
      int a = stack.pop();
      int b = stack.pop();
      //printf("%d * %d \n",a,b);
      stack.push(a * b) ;

    }
    else if(c.compare("/")==0) {
      int a = stack.pop();
      int b = stack.pop();
      //printf("%d + %d \n",b,a);
      stack.push(b / a) ;
    }
    else {
      //printf("push %s\n",c.c_str());
      stack.push(atoi(c.c_str()));
    }
  }
  return stack.pop();
}



bool is_num(char c)
{
  if(c=='0'||
     c=='1'||
     c=='2'||
     c=='3'||
     c=='4'||
     c=='5'||
     c=='6'||
     c=='7'||
     c=='8'||
     c=='9') {
    return true;
  }
  else {
    return false;
  }
}  

std::vector<std::string> parse(std::string str)
{
  std::vector<std::string> retval;
  
  for (int i=0;i<str.size();i++) {
    char c = str[i];
    switch (c) {
    case '+': {
      retval.push_back("+");
      break;
    }
    case '-': {
      retval.push_back("-");
      break;
    }
    case '*': {
      retval.push_back("*");
      break;
    }
    case '/': {
      retval.push_back("/");
      break;
    }
    default : {
      if (is_num(c)) {
        std::string s;
        s+=c;
        i++;
        char c = str[i];
        while(is_num(c)) {
          s+=c;
          i++;
          c = str[i];
        }
        retval.push_back(s);
        i--;
      }
      
    }
    }
  }
  return retval;
}

int main()
{
  Stack<std::string> stack;
  std::string str;
  getline(std::cin,str);
  std::vector<std::string> v = parse(str);
  int ret = eval(v);
  std::cout << ret << std::endl;
  return 0;
}