Generate successor boards

[slidingtile] / sliding_tile_lib.cc

#include "sliding_tile_lib.h"

#include <cstdlib>
#include <istream>
#include <memory>
#include <ostream>
#include <stdexcept>
#include <vector>

signed char Step::adjacent[BOARD_SIZE][5] = {
  1,   4,   -1,  -1,  -1,
  0,   2,   5,   -1,  -1,
  1,   3,   6,   -1,  -1,
  2,   7,   -1,  -1,  -1,
  0,   5,   8,   -1,  -1,
  1,   4,   6,   9,   -1,
  2,   5,   7,   10,  -1,
  3,   6,   11,  -1,  -1,
  4,   9,   12,  -1,  -1,
  5,   8,   10,  13,  -1,
  6,   9,   11,  14,  -1,
  7,   10,  15,  -1,  -1,
  8,   13,  -1,  -1,  -1,
  9,   12,  14,  -1,  -1,
  10,  13,  15,  -1,  -1,
  11,  14,  -1,  -1,  -1,
};

bool Board::is_valid() const {
  bool seen[BOARD_SIZE];
  for (int i = 0; i < BOARD_SIZE; i++) {
    seen[i] = false;
  }

  for (int i = 0; i < BOARD_SIZE; i++) {
    if (board[i] < 0 || board[i] >= BOARD_SIZE || seen[board[i]]) {
      return false;
    }
    seen[board[i]] = true;
  }

  // Redundant because pigeon-hole-principle, but check anyway
  for (int i = 0; i < BOARD_SIZE; i++) {
    if (!seen[i]) {
      return false;
    }
  }

  return true;
}

std::istream& operator>>(std::istream& is, Board& board) {
  for (int i = 0; i < BOARD_SIZE; i++) {
    if (!is.good()) {
      is.setstate(std::istream::failbit);
      break;
    }
    if (i > 0 && is.get() != ',') {
      is.setstate(std::istream::failbit);
      break;
    }
    int numeric;
    is >> numeric;
    board.board[i] = numeric;
  }
  if (!board.is_valid()) {
    is.setstate(std::istream::failbit);
  }
  return is;
}

std::ostream& operator<<(std::ostream& os, const Board& board) {
  for (int i = 0; i < BOARD_SIZE; i++) {
    if (i > 0) {
      os << " ";
    }
    os << int(board.board[i]);
  }
  return os;
}

signed char Board::hole() const {
  for (int i = 0; i < BOARD_SIZE; i++) {
    if (board[i] == 0) {
      return i;
    }
  }
  throw std::runtime_error("Board with no hole");
}

InvertedBoard Board::invert() const {
  InvertedBoard inv;
  for (int i = 0; i < BOARD_SIZE; i++) {
    inv.pos[board[i]] = i;
  }
  return inv;
}

int Board::distance(const Board& o) const {
  return distance(o.invert());
}

int Board::distance(const InvertedBoard& invo) const {
  int dist = 0;
  for (int i = 0; i < BOARD_SIZE; i++) {
    dist += std::abs(i % BOARD_DIM - invo.pos[board[i]] % BOARD_DIM) +
            std::abs(i / BOARD_DIM - invo.pos[board[i]] / BOARD_DIM);
  }
  return dist;
}

std::vector<Step*> Step::successors(std::shared_ptr<Step> shared_this) {
  std::vector<Step*> suc;
  signed char hole_pos = board.hole();
  for (int i = 0; adjacent[hole_pos][i] > 0; i++) {
    suc.emplace_back(new Step{board, shared_this});
    std::swap(suc.back()->board.board[hole_pos], suc.back()->board.board[adjacent[hole_pos][i]]);
  }
  return suc;
}