UVa 10284 - Chessboard in FEN

Accepted date: 2013-09-15
Ranking (as of 2013-09-15): 160 out of 757
Language: C++

/*
  UVa 10284 - Chessboard in FEN

  To build using Visual Studio 2012:
    cl -EHsc -O2 UVa_10284_Chessboard_in_FEN.cpp
*/

#include <cstdio>
#include <cstring>
#include <cctype>

const int nr_rows = 8, nr_columns = 8;
char chessboard[nr_rows][nr_columns], fen[nr_rows * (nr_columns + 1) + 1];

bool attack(int r, int c)
{
  if (r < 0 || r >= nr_rows || c < 0 || c >= nr_columns ||
    isalpha(chessboard[r][c]))
    return false;
  chessboard[r][c] = '+';
  return true;
}

void king_attack(int r, int c)
{
  for (int ri = r - 1; ri <= r + 1; ri++)
    for (int ci = c - 1; ci <= c + 1; ci++)
      if (ri != r || ci != c)
        attack(ri, ci);
}

void rook_attack(int r, int c)
{
  int ri, ci;
  for (ri = r - 1; ; ri--)
    if (!attack(ri, c))
      break;
  for (ri = r + 1; ; ri++)
    if (!attack(ri, c))
      break;
  for (ci = c - 1; ; ci--)
    if (!attack(r, ci))
      break;
  for (ci = c + 1; ; ci++)
    if (!attack(r, ci))
      break;
}

void bishop_attack(int r, int c)
{
  int ri, ci;
  for (ri = r - 1, ci = c - 1; ; ri--, ci--)
    if (!attack(ri, ci))
      break;
  for (ri = r - 1, ci = c + 1; ; ri--, ci++)
    if (!attack(ri, ci))
      break;
  for (ri = r + 1, ci = c - 1; ; ri++, ci--)
    if (!attack(ri, ci))
      break;
  for (ri = r + 1, ci = c + 1; ; ri++, ci++)
    if (!attack(ri, ci))
      break;
}

void knight_attack(int r, int c)
{
  attack(r - 2, c - 1);
  attack(r - 2, c + 1);
  attack(r - 1, c - 2);
  attack(r - 1, c + 2);
  attack(r + 1, c - 2);
  attack(r + 1, c + 2);
  attack(r + 2, c - 1);
  attack(r + 2, c + 1);
}

#ifdef DEBUG
void print_chessboard()
{
  for (int r = 0; r < nr_rows; r++)
    for (int c = 0; c < nr_columns; c++)
    printf("%c%c", chessboard[r][c], ((c == nr_columns - 1) ? '\n' : ' '));
}
#endif

int main()
{
  while (scanf("%s", fen) != EOF) {
    memset(chessboard, '-', sizeof(chessboard));
    int r = 0, c = 0;
    for (const char* p = fen; *p; p++) {
      if (*p == '/') {
        r++; c = 0;
      }
      else if (isdigit(*p))
        c += *p - '0';
      else
        chessboard[r][c++] = *p;
    }
    for (r = 0; r < nr_rows; r++)
      for (c = 0; c < nr_columns; c++) {
        switch (chessboard[r][c]) {
        case 'k': case 'K':
          king_attack(r, c);
          break;
        case 'q': case 'Q':
          rook_attack(r, c);
          bishop_attack(r, c);
          break;
        case 'b': case 'B':
          bishop_attack(r, c);
          break;
        case 'n': case 'N':
          knight_attack(r, c);
          break;
        case 'r': case 'R':
          rook_attack(r, c);
          break;
        case 'p':
          attack(r + 1, c - 1);
          attack(r + 1, c + 1);
          break;
        case 'P':
          attack(r - 1, c - 1);
          attack(r - 1, c + 1);
          break;
        }
#ifdef DEBUG
        if (isalpha(chessboard[r][c])) {
          printf("%d %d: %c\n", r, c, chessboard[r][c]);
          print_chessboard();
        }
#endif
      }
    int nr_unoccupied = 0;
    for (r = 0; r < nr_rows; r++)
      for (c = 0; c < nr_columns; c++)
        if (chessboard[r][c] == '-')
          nr_unoccupied++;
    printf("%d\n", nr_unoccupied);
  }
  return 0;
}