UVa 416 - LED Test

Accepted date: 2013-09-14
Ranking (as of 2013-09-14): 312 out of 754
Language: C++

/*
  UVa 416 - LED Test

  To build using Visual Studio 2012:
    cl -EHsc -O2 UVa_416_LED_Test.cpp
*/

#include <cstdio>

const unsigned char leds[] =
  {0x7e, 0x30, 0x6d, 0x79, 0x33, 0x5b, 0x5f, 0x70, 0x7f, 0x7b};
const int n_max = sizeof(leds);

unsigned char s_to_sequence(const char* s)
{
  unsigned char sq = 0, b = 0x40;
  do {
    if (*s++ == 'Y')
      sq |= b;
    b >>= 1;
  } while (b);
  return sq;
}

bool match_sequence(int n, unsigned char sequence[])
{
  for (int ns = n_max; ns >= n; ns--) {
    bool match = true;
    unsigned char not_burned = 0x7f;
    for (int i = 1; i <= n; i++) {
      unsigned char led = leds[ns - i];
      led &= not_burned;
      unsigned char diff = led ^ sequence[i - 1];
      unsigned char db = diff, lb = led;
      for ( ; db; db >>= 1, lb >>= 1)
        if (db & 1 && !(lb & 1))
          break; // no burned-out segments will recover
      if (db) {
        match = false; break;
      }
      not_burned &= ~diff;
    }
    if (match)
      return true;
  }
  return false;
}

int main()
{
  while (true) {
    int n;
    scanf("%d", &n);
    if (!n)
      break;
    unsigned char sequence[n_max];
    for (int i = 0; i < n; i++) {
      char s[7 + 1];
      scanf("%s", s);
      sequence[i] = s_to_sequence(s);
    }
    if (match_sequence(n, sequence))
      puts("MATCH");
    else
      puts("MISMATCH");
  }
  return 0;
}