2015-day24: combinations, a lot of assumptions can be made about the input shape

2015/day24/main.go

@@ -1,10 +1,14 @@
+// TODO: pull combinations, multiplying a slice of ints, into algos and mathy packages?
 package main
 
 import (
 	"flag"
 	"fmt"
+	"sort"
 	"strings"
 
+	"github.com/alexchao26/advent-of-code-go/mathy"
+
 	"github.com/alexchao26/advent-of-code-go/cast"
 	"github.com/alexchao26/advent-of-code-go/util"
 )
@@ -15,32 +19,73 @@ func main() {
 	flag.Parse()
 	fmt.Println("Running part", part)
 
-	if part == 1 {
-		ans := part1(util.ReadFile("./input.txt"))
-		util.CopyToClipboard(fmt.Sprintf("%v", ans))
-		fmt.Println("Output:", ans)
-	} else {
-		ans := part2(util.ReadFile("./input.txt"))
-		util.CopyToClipboard(fmt.Sprintf("%v", ans))
-		fmt.Println("Output:", ans)
+	ans := balancingPackages(util.ReadFile("./input.txt"), part)
+	fmt.Println("Output:", ans)
+}
+
+func balancingPackages(input string, part int) int {
+	var nums []int
+	for _, line := range strings.Split(input, "\n") {
+		nums = append(nums, cast.ToInt(line))
 	}
-}
 
-func part1(input string) int {
-	parsed := parseInput(input)
-	_ = parsed
+	sum := mathy.SumIntSlice(nums)
 
-	return 0
-}
-
-func part2(input string) int {
-	return 0
-}
-
-func parseInput(input string) (ans []int) {
-	lines := strings.Split(input, "\n")
-	for _, l := range lines {
-		ans = append(ans, cast.ToInt(l))
+	target := sum / 3
+	if part == 2 {
+		target = sum / 4
 	}
-	return ans
+
+	var individualGroups [][]int
+	for groupLen := 2; len(individualGroups) == 0; groupLen++ {
+		for i := 0; i < len(nums); i++ {
+			individualGroups = append(individualGroups, combinations(nums, groupLen, []int{}, i)...)
+		}
+
+		// validate that a combination adds up to the target sum
+		var validGroups [][]int
+		for _, gr := range individualGroups {
+			if mathy.SumIntSlice(gr) == target {
+				validGroups = append(validGroups, gr)
+			}
+		}
+		// reassign individual groups, if len(validGroups) == 0; we need to rerun
+		// with a larger groupLen
+		individualGroups = validGroups
+	}
+
+	individualGroups = sortGroups(individualGroups)
+
+	return quantumEntanglement(individualGroups[0])
+}
+
+func combinations(nums []int, length int, combo []int, index int) [][]int {
+	if len(combo) == length {
+		return [][]int{append([]int{}, combo...)}
+	}
+	var combos [][]int
+	for i := index; i < len(nums); i++ {
+		combo = append(combo, nums[i])
+		with := combinations(nums, length, combo, i+1)
+		combos = append(combos, with...)
+		// backtrack
+		combo = combo[:len(combo)-1]
+	}
+
+	return combos
+}
+
+func sortGroups(groups [][]int) [][]int {
+	sort.Slice(groups, func(i, j int) bool {
+		return quantumEntanglement(groups[i]) < quantumEntanglement(groups[j])
+	})
+	return groups
+}
+
+func quantumEntanglement(nums []int) int {
+	prod := 1
+	for _, n := range nums {
+		prod *= n
+	}
+	return prod
 }

2015/day24/main_test.go

@@ -2,37 +2,24 @@ package main
 
 import (
 	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
 )
 
-func Test_part1(t *testing.T) {
+func Test_balancingPackages(t *testing.T) {
 	tests := []struct {
 		name  string
 		input string
+		part  int
 		want  int
 	}{
-		// {"actual", util.ReadFile("input.txt"), ACTUAL_ANSWER},
+		{"part1 actual", util.ReadFile("input.txt"), 1, 10439961859},
+		{"part2 actual", util.ReadFile("input.txt"), 2, 72050269},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			if got := part1(tt.input); got != tt.want {
-				t.Errorf("part1() = %v, want %v", got, tt.want)
-			}
-		})
-	}
-}
-
-func Test_part2(t *testing.T) {
-	tests := []struct {
-		name  string
-		input string
-		want  int
-	}{
-		// {"actual", util.ReadFile("input.txt"), ACTUAL_ANSWER},
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			if got := part2(tt.input); got != tt.want {
-				t.Errorf("part2() = %v, want %v", got, tt.want)
+			if got := balancingPackages(tt.input, tt.part); got != tt.want {
+				t.Errorf("balancingPackages() = %v, want %v", got, tt.want)
 			}
 		})
 	}