A distance metric

[slidingtile] / sliding_tile_lib.cc

diff --git a/sliding_tile_lib.cc b/sliding_tile_lib.cc
index 4b422c1721da721020713f6410a93b7a5f283edf..aee8380c421fe11036f4c9bc957cca971edf6eca 100644 (file)
--- a/sliding_tile_lib.cc
+++ b/sliding_tile_lib.cc
@@ -1,5 +1,10 @@
 #include "sliding_tile_lib.h"
 
+#include <cstdlib>
+#include <istream>
+#include <ostream>
+#include <stdexcept>
+
 signed char adjacent[BOARD_SIZE][5] = {
   1,   4,   -1,  -1,  -1,
   0,   2,   5,   -1,  -1,
@@ -18,3 +23,86 @@ signed char adjacent[BOARD_SIZE][5] = {
   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;
+}