From f3f55aff4e3346b297215050c2076c821fd60c83 Mon Sep 17 00:00:00 2001
From: Scott Worley <scottworley@scottworley.com>
Date: Thu, 31 Dec 2015 20:34:39 -0800
Subject: [PATCH] A where's-the-hole function.

---
 sliding_tile_lib.cc      | 10 ++++++++++
 sliding_tile_lib.h       |  1 +
 sliding_tile_lib_test.cc | 10 ++++++++++
 3 files changed, 21 insertions(+)

diff --git a/sliding_tile_lib.cc b/sliding_tile_lib.cc
index 3b7806b..b8ddc15 100644
--- a/sliding_tile_lib.cc
+++ b/sliding_tile_lib.cc
@@ -1,6 +1,7 @@
 #include "sliding_tile_lib.h"
 
 #include <istream>
+#include <stdexcept>
 
 signed char adjacent[BOARD_SIZE][5] = {
   1,   4,   -1,  -1,  -1,
@@ -63,3 +64,12 @@ std::istream& operator>>(std::istream& is, Board& board) {
   }
   return is;
 }
+
+signed char Board::hole() {
+  for (int i = 0; i < BOARD_SIZE; i++) {
+    if (board[i] == 0) {
+      return i;
+    }
+  }
+  throw std::runtime_error("Board with no hole");
+}
diff --git a/sliding_tile_lib.h b/sliding_tile_lib.h
index 89c65c1..84d422e 100644
--- a/sliding_tile_lib.h
+++ b/sliding_tile_lib.h
@@ -9,6 +9,7 @@ const int BOARD_SIZE = BOARD_DIM * BOARD_DIM;
 struct Board {
   signed char board[BOARD_SIZE];
   bool is_valid();
+  signed char hole();
 };
 std::istream& operator>>(std::istream& is, Board& board);
 
diff --git a/sliding_tile_lib_test.cc b/sliding_tile_lib_test.cc
index 7f032a4..12cc46b 100644
--- a/sliding_tile_lib_test.cc
+++ b/sliding_tile_lib_test.cc
@@ -76,3 +76,13 @@ TEST(Board, HighTileInput) {
   is >> b;
   EXPECT_TRUE(is.fail());
 }
+
+TEST(Board, Hole) {
+  Board b{{16,14,9,13,3,1,12,8,0,11,6,4,7,5,2,10}};
+  EXPECT_EQ(8, b.hole());
+}
+
+TEST(Board, NoHole) {
+  Board b{{16,14,9,13,3,1,12,8,16,11,6,4,7,5,2,10}};
+  EXPECT_THROW(b.hole(), std::runtime_error);
+}
-- 
2.44.1