UVa 759 - The Return of the Roman Empire

Accepted date: 2015-04-15
Ranking (as of 2015-04-15): 157 out of 445
Language: C++

/*
  UVa 759 - The Return of the Roman Empire

  To build using Visual Studio 2012:
    cl -EHsc -O2 UVa_759_The_Return_of_the_Roman_Empire.cpp
*/

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

int roman_numeral(const char* s)
{
  int n = 0;
  while (*s) {
    const char* ns = s + 1;
    int d = 0;
    switch (*s) {
    case 'I':
      if (n % 10)
        return -1;
      if (*ns && (*ns == 'V' || *ns == 'X')) {
        d = (*ns == 'V') ? 4 : 9;
        ns++;
      }
      else {
        d++;
        while (*ns && *ns == 'I') {
          if (++ns - s > 3)
            return -1;
          d++;
        }
      }
      break;
    case 'V':
      if (n % 10)
        return -1;
      d = 5;
      while (*ns && *ns == 'I') {
        if (++ns - s > 4)
          return -1;
        d++;
      }
      break;
    case 'X':
      if ((n % 100) / 10 || n % 10)
        return -1;
      if (*ns && (*ns == 'L' || *ns == 'C')) {
        d = (*ns == 'L') ? 40 : 90;
        ns++;
      }
      else {
        d = 10;
        while (*ns && *ns == 'X') {
          if (++ns - s > 3)
            return -1;
          d += 10;
        }
      }
      break;
    case 'L':
      if ((n % 100) / 10 || n % 10)
        return -1;
      d = 50;
      while (*ns && *ns == 'X') {
        if (++ns - s > 4)
          return -1;
        d += 10;
      }
      break;
    case 'C':
      if ((n % 1000) / 100 || n % 100)
        return -1;
      if (*ns && (*ns == 'D' || *ns == 'M')) {
        d = (*ns == 'D') ? 400 : 900;
        ns++;
      }
      else {
        d = 100;
        while (*ns && *ns == 'C') {
          if (++ns - s > 3)
            return -1;
          d += 100;
        }
      }
      break;
    case 'D':
      if ((n % 1000) / 100 || n % 100)
        return -1;
      d = 500;
      while (*ns && *ns == 'C') {
        if (++ns - s > 4)
          return -1;
        d += 100;
      }
      break;
    case 'M':
      if (n / 1000 || n % 1000)
        return -1;
      d = 1000;
      while (*ns && *ns == 'M') {
        if (++ns - s > 3)
          return -1;
        d += 1000;
      }
      break;
    default:
      return -1;
    }
    n += d;
    s = ns;
  }
  return n;
}

int main()
{
  string s;
  while (getline(cin, s)) {
    int n = roman_numeral(s.c_str());
    if (n >= 0)
      cout << n << endl;
    else
      cout << "This is not a valid number\n";
  }
  return 0;
}