X-Git-Url: http://git.scottworley.com/slidingtile/blobdiff_plain/32688d85f745574d7bbf941985234458d2776cce..b18667f24728cb960b0c60fa55824062582278bf:/sliding_tile_lib.cc?ds=sidebyside

diff --git a/sliding_tile_lib.cc b/sliding_tile_lib.cc
index a4d522e..3b7806b 100644
--- a/sliding_tile_lib.cc
+++ b/sliding_tile_lib.cc
@@ -21,6 +21,29 @@ signed char adjacent[BOARD_SIZE][5] = {
   11,  14,  -1,  -1,  -1,
 };
 
+bool Board::is_valid() {
+  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()) {
@@ -33,7 +56,10 @@ std::istream& operator>>(std::istream& is, Board& board) {
     }
     int numeric;
     is >> numeric;
-    board[i] = numeric;
+    board.board[i] = numeric;
+  }
+  if (!board.is_valid()) {
+    is.setstate(std::istream::failbit);
   }
   return is;
 }