Add "EliminatedBy" to snake eliminations. (#11)

* add eliminated by

* add test

* make sure largest snake is listed as eliminator on head to head collisions

* remove unused type def

* Reduce memory usage during elimination checks.

Co-authored-by: Daniel Steuernol <dlsteuer@gmail.com>

go.sum

@@ -5,6 +5,7 @@ github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZN
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

ruleset.go

@@ -17,6 +17,7 @@ type Snake struct {
 	Body            []Point
 	Health          int32
 	EliminatedCause string
+	EliminatedBy    string
 }
 
 type BoardState struct {

standard.go

@@ -3,6 +3,7 @@ package rules
 import (
 	"errors"
 	"math/rand"
+	"sort"
 )
 
 type StandardRuleset struct{}
@@ -256,6 +257,19 @@ func (r *StandardRuleset) reduceSnakeHealth(b *BoardState) error {
 }
 
 func (r *StandardRuleset) eliminateSnakes(b *BoardState) error {
+	// First order snake indices by length.
+	// In multi-collision scenarios we want to always attribute elimination to the longest snake.
+	snakeIndicesByLength := make([]int, len(b.Snakes))
+	for i := 0; i < len(b.Snakes); i++ {
+		snakeIndicesByLength[i] = i
+	}
+	sort.Slice(snakeIndicesByLength, func(i int, j int) bool {
+		lenI := len(b.Snakes[snakeIndicesByLength[i]].Body)
+		lenJ := len(b.Snakes[snakeIndicesByLength[j]].Body)
+		return lenI > lenJ
+	})
+
+	// Iterate through snakes checking for eliminations.
 	for i := 0; i < len(b.Snakes); i++ {
 		snake := &b.Snakes[i]
 		if len(snake.Body) <= 0 {
@@ -273,14 +287,15 @@ func (r *StandardRuleset) eliminateSnakes(b *BoardState) error {
 		}
 
 		// Always check body collisions before head-to-heads
-		for j := 0; j < len(b.Snakes); j++ {
-			other := &b.Snakes[j]
+		for _, otherIndex := range snakeIndicesByLength {
+			other := &b.Snakes[otherIndex]
 			if r.snakeHasBodyCollided(snake, other) {
 				if snake.ID == other.ID {
 					snake.EliminatedCause = EliminatedBySelfCollision
 				} else {
 					snake.EliminatedCause = EliminatedByCollision
 				}
+				snake.EliminatedBy = other.ID
 				break
 			}
 		}
@@ -288,11 +303,12 @@ func (r *StandardRuleset) eliminateSnakes(b *BoardState) error {
 			continue
 		}
 
-		// Always check body collisions before head-to-heads
-		for j := 0; j < len(b.Snakes); j++ {
-			other := &b.Snakes[j]
+		// Always check head-to-heads after body collisions
+		for _, otherIndex := range snakeIndicesByLength {
+			other := &b.Snakes[otherIndex]
 			if snake.ID != other.ID && r.snakeHasLostHeadToHead(snake, other) {
 				snake.EliminatedCause = EliminatedByHeadToHeadCollision
+				snake.EliminatedBy = other.ID
 				break
 			}
 		}

standard_test.go

@@ -763,61 +763,78 @@ func TestSnakeHasLostHeadToHead(t *testing.T) {
 
 func TestEliminateSnakes(t *testing.T) {
 	tests := []struct {
+		Name                     string
 		Snakes                   []Snake
 		ExpectedEliminatedCauses []string
+		ExpectedEliminatedBy     []string
 		Err                      error
 	}{
 		{
+			"Empty",
 			[]Snake{},
 			[]string{},
+			[]string{},
 			nil,
 		},
 		{
+			"Zero Snake",
 			[]Snake{
 				Snake{},
 			},
 			[]string{NotEliminated},
+			[]string{""},
 			errors.New("snake is length zero"),
 		},
 		{
+			"Single Starvation",
 			[]Snake{
-				Snake{Body: []Point{{1, 1}}},
+				Snake{ID: "1", Body: []Point{{1, 1}}},
 			},
 			[]string{EliminatedByStarvation},
+			[]string{""},
 			nil,
 		},
 		{
+			"Not Eliminated",
 			[]Snake{
-				Snake{Health: 1, Body: []Point{{1, 1}}},
+				Snake{ID: "1", Health: 1, Body: []Point{{1, 1}}},
 			},
 			[]string{NotEliminated},
+			[]string{""},
 			nil,
 		},
 		{
+			"Out of Bounds",
 			[]Snake{
-				Snake{Health: 1, Body: []Point{{-1, 1}}},
+				Snake{ID: "1", Health: 1, Body: []Point{{-1, 1}}},
 			},
 			[]string{EliminatedByOutOfBounds},
+			[]string{""},
 			nil,
 		},
 		{
+			"Self Collision",
 			[]Snake{
-				Snake{Health: 1, Body: []Point{{0, 0}, {0, 1}, {0, 0}}},
+				Snake{ID: "1", Health: 1, Body: []Point{{0, 0}, {0, 1}, {0, 0}}},
 			},
 			[]string{EliminatedBySelfCollision},
+			[]string{"1"},
 			nil,
 		},
 		{
+			"Multiple Separate Deaths",
 			[]Snake{
-				Snake{Health: 1, Body: []Point{{0, 0}, {0, 1}, {0, 0}}},
-				Snake{Health: 1, Body: []Point{{-1, 1}}},
+				Snake{ID: "1", Health: 1, Body: []Point{{0, 0}, {0, 1}, {0, 0}}},
+				Snake{ID: "2", Health: 1, Body: []Point{{-1, 1}}},
 			},
 			[]string{
 				EliminatedBySelfCollision,
 				EliminatedByOutOfBounds},
+			[]string{"1", ""},
 			nil,
 		},
 		{
+			"Other Collision",
 			[]Snake{
 				Snake{ID: "1", Health: 1, Body: []Point{{0, 2}, {0, 3}, {0, 4}}},
 				Snake{ID: "2", Health: 1, Body: []Point{{0, 0}, {0, 1}, {0, 2}}},
@@ -825,9 +842,11 @@ func TestEliminateSnakes(t *testing.T) {
 			[]string{
 				EliminatedByCollision,
 				NotEliminated},
+			[]string{"2", ""},
 			nil,
 		},
 		{
+			"All Eliminated Head 2 Head",
 			[]Snake{
 				Snake{ID: "1", Health: 1, Body: []Point{{1, 1}}},
 				Snake{ID: "2", Health: 1, Body: []Point{{1, 1}}},
@@ -838,9 +857,11 @@ func TestEliminateSnakes(t *testing.T) {
 				EliminatedByHeadToHeadCollision,
 				EliminatedByHeadToHeadCollision,
 			},
+			[]string{"2", "1", "1"},
 			nil,
 		},
 		{
+			"One Snake wins Head 2 Head",
 			[]Snake{
 				Snake{ID: "1", Health: 1, Body: []Point{{1, 1}, {0, 1}}},
 				Snake{ID: "2", Health: 1, Body: []Point{{1, 1}, {1, 2}, {1, 3}}},
@@ -851,9 +872,11 @@ func TestEliminateSnakes(t *testing.T) {
 				NotEliminated,
 				EliminatedByHeadToHeadCollision,
 			},
+			[]string{"2", "", "2"},
 			nil,
 		},
 		{
+			"All Snakes Body Eliminated",
 			[]Snake{
 				Snake{ID: "1", Health: 1, Body: []Point{{4, 4}, {3, 3}}},
 				Snake{ID: "2", Health: 1, Body: []Point{{3, 3}, {2, 2}}},
@@ -868,9 +891,11 @@ func TestEliminateSnakes(t *testing.T) {
 				EliminatedByCollision,
 				EliminatedByCollision,
 			},
+			[]string{"4", "1", "2", "3", "4"},
 			nil,
 		},
 		{
+			"All Snakes Eliminated Head 2 Head",
 			[]Snake{
 				Snake{ID: "1", Health: 1, Body: []Point{{4, 4}, {4, 5}}},
 				Snake{ID: "2", Health: 1, Body: []Point{{4, 4}, {4, 3}}},
@@ -883,9 +908,11 @@ func TestEliminateSnakes(t *testing.T) {
 				EliminatedByHeadToHeadCollision,
 				EliminatedByHeadToHeadCollision,
 			},
+			[]string{"2", "1", "1", "1"},
 			nil,
 		},
 		{
+			"4 Snakes Head 2 Head",
 			[]Snake{
 				Snake{ID: "1", Health: 1, Body: []Point{{4, 4}, {4, 5}}},
 				Snake{ID: "2", Health: 1, Body: []Point{{4, 4}, {4, 3}}},
@@ -898,12 +925,14 @@ func TestEliminateSnakes(t *testing.T) {
 				NotEliminated,
 				EliminatedByHeadToHeadCollision,
 			},
+			[]string{"3", "3", "", "3"},
 			nil,
 		},
 	}
 
 	r := StandardRuleset{}
 	for _, test := range tests {
+		t.Run(test.Name, func(t *testing.T) {
 			b := &BoardState{
 				Width:  10,
 				Height: 10,
@@ -911,9 +940,11 @@ func TestEliminateSnakes(t *testing.T) {
 			}
 			err := r.eliminateSnakes(b)
 			require.Equal(t, test.Err, err)
-		for i := 0; i < len(b.Snakes); i++ {
-			require.Equal(t, test.ExpectedEliminatedCauses[i], b.Snakes[i].EliminatedCause)
+			for i, snake := range b.Snakes {
+				require.Equal(t, test.ExpectedEliminatedCauses[i], snake.EliminatedCause)
+				require.Equal(t, test.ExpectedEliminatedBy[i], snake.EliminatedBy)
 			}
+		})
 	}
 }