From 2c35054f652f2d4bbf09867a871096f48e5c7af8 Mon Sep 17 00:00:00 2001
From: Scott Worley <scottworley@scottworley.com>
Date: Mon, 28 Dec 2015 17:35:41 -0800
Subject: [PATCH] Adjacent spaces

---
 sliding_tile.go      | 30 +++++++++++++++++++++++++++++-
 sliding_tile_test.go | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/sliding_tile.go b/sliding_tile.go
index 32bccae..96e00dc 100644
--- a/sliding_tile.go
+++ b/sliding_tile.go
@@ -5,11 +5,19 @@ import "os"
 import "strconv"
 
 const HOLE = 0
-const BOARD_SIZE = 16
+const BOARD_DIM = 4
+const BOARD_SIZE = BOARD_DIM * BOARD_DIM
 
 type Space int8
 type Board [BOARD_SIZE]Space
 
+const (
+	LEFT  = -1
+	RIGHT = +1
+	UP    = -BOARD_DIM
+	DOWN  = +BOARD_DIM
+)
+
 func read_board_from_strings(in []string) (*Board, error) {
 	if len(in) != BOARD_SIZE {
 		return nil, fmt.Errorf("Please provide %d values", BOARD_SIZE)
@@ -25,6 +33,26 @@ func read_board_from_strings(in []string) (*Board, error) {
 	return &b, nil
 }
 
+func adjacent_spaces(s Space) []Space {
+	if s < 0 || s >= BOARD_SIZE {
+		panic("Invalid space")
+	}
+	var adjacent []Space
+	if s >= BOARD_DIM {
+		adjacent = append(adjacent, s+UP)
+	}
+	if s < BOARD_SIZE-BOARD_DIM {
+		adjacent = append(adjacent, s+DOWN)
+	}
+	if s%BOARD_DIM != 0 {
+		adjacent = append(adjacent, s+LEFT)
+	}
+	if s%BOARD_DIM != BOARD_DIM-1 {
+		adjacent = append(adjacent, s+RIGHT)
+	}
+	return adjacent
+}
+
 func main() {
 	start, err := read_board_from_strings(os.Args[1:])
 	if err != nil {
diff --git a/sliding_tile_test.go b/sliding_tile_test.go
index 28392ee..34f3fcc 100644
--- a/sliding_tile_test.go
+++ b/sliding_tile_test.go
@@ -1,5 +1,7 @@
 package main
 
+import "reflect"
+import "sort"
 import "testing"
 
 func Test_read_board_from_strings(t *testing.T) {
@@ -26,3 +28,43 @@ func Test_read_board_from_strings(t *testing.T) {
 		t.Fail()
 	}
 }
+
+// For sorting, for unordered equality testing
+type Spaces []Space
+
+func (s Spaces) Len() int           { return len(s) }
+func (s Spaces) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+func (s Spaces) Less(i, j int) bool { return s[i] < s[j] }
+
+func Test_adjacent_spaces(t *testing.T) {
+	type TestCase struct {
+		s        Space
+		expected Spaces
+	}
+	cases := []TestCase{
+		{0, []Space{1, 4}},
+		{1, []Space{0, 2, 5}},
+		{2, []Space{1, 3, 6}},
+		{3, []Space{2, 7}},
+		{4, []Space{0, 5, 8}},
+		{5, []Space{1, 4, 6, 9}},
+		{6, []Space{2, 5, 7, 10}},
+		{7, []Space{3, 6, 11}},
+		{8, []Space{4, 9, 12}},
+		{9, []Space{5, 8, 10, 13}},
+		{10, []Space{6, 9, 11, 14}},
+		{11, []Space{7, 10, 15}},
+		{12, []Space{8, 13}},
+		{13, []Space{9, 12, 14}},
+		{14, []Space{10, 13, 15}},
+		{15, []Space{11, 14}},
+	}
+	for i, c := range cases {
+		var actual Spaces = adjacent_spaces(c.s)
+		sort.Sort(c.expected)
+		sort.Sort(actual)
+		if !reflect.DeepEqual(c.expected, actual) {
+			t.Error(i, c.expected, actual)
+		}
+	}
+}
-- 
2.44.1