Merge pull request #89 from vaskoz/day39

Day39

README.md

@@ -50,4 +50,5 @@ problems from
 * [Day 36](https://github.com/vaskoz/dailycodingproblem-go/issues/79)
 * [Day 37](https://github.com/vaskoz/dailycodingproblem-go/issues/81)
 * [Day 38](https://github.com/vaskoz/dailycodingproblem-go/issues/83)
+* [Day 39](https://github.com/vaskoz/dailycodingproblem-go/issues/84)
 * [Day 40](https://github.com/vaskoz/dailycodingproblem-go/issues/87)

day39/problem.go

@@ -0,0 +1,130 @@
+package day39
+
+import (
+	"math"
+	"strings"
+)
+
+// Coord represents a coordinate in the game of life.
+type Coord struct {
+	X, Y int64
+}
+
+// GameOfLife represents the game state.
+// '*' represents a live cell and '.' represents a dead cell.
+type GameOfLife struct {
+	living                 map[Coord]struct{}
+	minX, minY, maxX, maxY int64
+}
+
+// NewGameOfLife parses a starting board.
+// The given board's lower left coordinate with be 0,0
+func NewGameOfLife(board string) *GameOfLife {
+	gol := &GameOfLife{living: make(map[Coord]struct{})}
+	rows := strings.Split(board, "\n")
+	gol.maxY = int64(len(rows))
+	for y := 0; y < len(rows); y++ {
+		for x, val := range rows[len(rows)-1-y] {
+			if val == '*' {
+				gol.living[Coord{int64(x), int64(y)}] = struct{}{}
+				if int64(x) >= gol.maxX {
+					gol.maxX = int64(x) + 1
+				}
+			}
+		}
+	}
+	gol.minX, gol.minY = -1, -1
+	return gol
+}
+
+// String returns the string representation of the board now.
+func (gol *GameOfLife) String() string {
+	var sb strings.Builder
+	for y := gol.maxY - 1; y > gol.minY; y-- {
+		for x := gol.minX + 1; x < gol.maxX; x++ {
+			if _, alive := gol.living[Coord{x, y}]; alive {
+				sb.WriteRune('*')
+			} else {
+				sb.WriteRune('.')
+			}
+		}
+		sb.WriteRune('\n')
+	}
+	return sb.String()
+}
+
+// Step executes a single step of the simulation.
+func (gol *GameOfLife) Step() {
+	var birth, death []Coord
+	for coord := range gol.living {
+		if gol.willDie(coord) {
+			death = append(death, coord)
+		}
+		birth = append(birth, gol.willBeBorn(coord)...)
+	}
+	for _, d := range death {
+		delete(gol.living, d)
+	}
+	for _, b := range birth {
+		gol.living[b] = struct{}{}
+	}
+	gol.minX, gol.minY, gol.maxX, gol.maxY = math.MaxInt64, math.MaxInt64, math.MinInt64, math.MinInt64
+	for coord := range gol.living {
+		if coord.X <= gol.minX {
+			gol.minX = coord.X - 1
+		}
+		if coord.X >= gol.maxX {
+			gol.maxX = coord.X + 1
+		}
+		if coord.Y <= gol.minY {
+			gol.minY = coord.Y - 1
+		}
+		if coord.Y >= gol.maxY {
+			gol.maxY = coord.Y + 1
+		}
+	}
+}
+
+func (gol *GameOfLife) livingNeighbors(coord Coord) int {
+	var livingNeighbors int
+	for x := coord.X - 1; x <= coord.X+1; x++ {
+		for y := coord.Y - 1; y <= coord.Y+1; y++ {
+			if x == coord.X && y == coord.Y {
+				continue
+			}
+			if _, alive := gol.living[Coord{x, y}]; alive {
+				livingNeighbors++
+			}
+		}
+	}
+	return livingNeighbors
+}
+
+func (gol *GameOfLife) willBeBorn(coord Coord) []Coord {
+	var birth []Coord
+	checked := make(map[Coord]struct{})
+	for x := coord.X - 1; x <= coord.X+1; x++ {
+		for y := coord.Y - 1; y <= coord.Y+1; y++ {
+			if x == coord.X && y == coord.Y {
+				continue
+			}
+			coord := Coord{x, y}
+			if _, alive := gol.living[coord]; alive {
+				continue
+			}
+			if _, done := checked[coord]; !done {
+				checked[coord] = struct{}{}
+				living := gol.livingNeighbors(coord)
+				if living == 3 {
+					birth = append(birth, coord)
+				}
+			}
+		}
+	}
+	return birth
+}
+
+func (gol *GameOfLife) willDie(coord Coord) bool {
+	living := gol.livingNeighbors(coord)
+	return living < 2 || living > 3
+}

day39/problem_test.go

@@ -0,0 +1,40 @@
+package day39
+
+import "testing"
+
+var testcases = []struct {
+	board    string
+	steps    int
+	expected string
+}{
+	{"*\n*\n*", 1, "***\n"},
+	{"*\n*\n*", 2, "*\n*\n*\n"},
+	{"**\n**", 2, "**\n**\n"},
+	{"**\n*.", 1, "**\n**\n"},
+	{"..*\n.*.\n*..", 1, "*\n"},
+	{"**.\n*.*\n.*.", 2, "**.\n*.*\n.*.\n"},
+	{"**.\n*.*\n.*.", 20, "**.\n*.*\n.*.\n"},
+}
+
+func TestGameOfLife(t *testing.T) {
+	t.Parallel()
+	for n, tc := range testcases {
+		gol := NewGameOfLife(tc.board)
+		for i := 0; i < tc.steps; i++ {
+			gol.Step()
+		}
+		if result := gol.String(); result != tc.expected {
+			t.Errorf("TC%d Expected %v got %v", n, tc.expected, result)
+		}
+	}
+}
+
+func BenchmarkGameOfLife(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			gol := NewGameOfLife(tc.board)
+			gol.Step()
+			_ = gol.String()
+		}
+	}
+}