feat: Add Tic Tac Toe winning algorithm. (#7)

Author: goloroden

README.md

@@ -11,6 +11,7 @@ So far, the following exercises have been covered:
 - [Heap](./heap/) – implements a heap from scratch, without using the built-in `container/heap` package
 - [Remove k-th last element](./removekthlastelement/) – removes the k-th last element from a single-linked list
 - [Running median](./runningmedian/) – calculates the running median of a sequence of numbers
+- [Tic tac toe](./tictactoe/) – detects winnning states in a tic tac toe game
 
 ## Running quality assurance
 

tictactoe/documentation.go

@@ -0,0 +1,2 @@
+// Package tictactoe detects winnning states in a tic tac toe game.
+package tictactoe

tictactoe/tictactoe.go

@@ -0,0 +1,35 @@
+package tictactoe
+
+type Field struct {
+	Row    int
+	Column int
+}
+
+func HasWon(fields []Field, size int) bool {
+	rowSums := make([]int, size)
+	columnSums := make([]int, size)
+
+	slashDiagonalSum := 0
+	backslashDiagonalSum := 0
+
+	for _, field := range fields {
+		rowSums[field.Row]++
+		columnSums[field.Column]++
+
+		if field.Row == field.Column {
+			slashDiagonalSum++
+		}
+		if field.Row == size-field.Column-1 {
+			backslashDiagonalSum++
+		}
+
+		if rowSums[field.Row] == size ||
+			columnSums[field.Column] == size ||
+			slashDiagonalSum == size ||
+			backslashDiagonalSum == size {
+			return true
+		}
+	}
+
+	return false
+}

tictactoe/tictactoe_test.go

@@ -0,0 +1,67 @@
+package tictactoe_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/thenativeweb/codingcircle/tictactoe"
+)
+
+func TestHasWon(t *testing.T) {
+	testCases := []struct {
+		name   string
+		fields []tictactoe.Field
+		size   int
+		hasWon bool
+	}{
+		{
+			name:   "Returns false for an empty board.",
+			fields: []tictactoe.Field{},
+			size:   3,
+			hasWon: false,
+		},
+		{
+			name:   "Returns false for a board with a single field.",
+			fields: []tictactoe.Field{{0, 0}},
+			size:   3,
+			hasWon: false,
+		},
+		{
+			name:   "Returns true for a row on a 3x3 board.",
+			fields: []tictactoe.Field{{0, 0}, {0, 1}, {0, 2}},
+			size:   3,
+			hasWon: true,
+		},
+		{
+			name:   "Returns true for a column on a 3x3 board.",
+			fields: []tictactoe.Field{{0, 0}, {1, 0}, {2, 0}},
+			size:   3,
+			hasWon: true,
+		},
+		{
+			name:   "Returns true for the slash diagonal on a 3x3 board.",
+			fields: []tictactoe.Field{{0, 1}, {0, 2}, {1, 0}, {1, 1}, {2, 0}, {2, 2}},
+			size:   3,
+			hasWon: true,
+		},
+		{
+			name:   "Returns true for the backslash diagonal on a 3x3 board.",
+			fields: []tictactoe.Field{{0, 0}, {0, 1}, {1, 1}, {1, 2}, {2, 0}, {2, 2}},
+			size:   3,
+			hasWon: true,
+		},
+		{
+			name:   "Returns true for a row on a 4x4 board.",
+			fields: []tictactoe.Field{{0, 0}, {0, 1}, {0, 2}, {0, 3}},
+			size:   4,
+			hasWon: true,
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			hasWon := tictactoe.HasWon(testCase.fields, testCase.size)
+			assert.Equal(t, testCase.hasWon, hasWon)
+		})
+	}
+}