2021 - Day 7

2021/7/go.mod

@@ -0,0 +1,9 @@
+module AoC/2021/7
+
+require AoC/2021/common v0.0.0
+
+require github.com/joho/godotenv v1.4.0 // indirect
+
+replace AoC/2021/common v0.0.0 => ../common
+
+go 1.17

2021/7/go.sum

@@ -0,0 +1,2 @@
+github.com/joho/godotenv v1.4.0 h1:3l4+N6zfMWnkbPEXKng2o2/MR5mSwTrBih4ZEkkz1lg=
+github.com/joho/godotenv v1.4.0/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=

2021/7/main.go

@@ -0,0 +1,62 @@
+package main
+
+import (
+	aoc "AoC/2021/common"
+	"bufio"
+	"strconv"
+	"strings"
+)
+
+func findMinFuel(cf func (distance int) int) func (*bufio.Scanner) int {
+	return func (input *bufio.Scanner) int {
+		max := 0
+		input.Scan()
+		crabs := make(map[int] int)
+		for _, s := range strings.Split(input.Text(), ",") {
+			n, err := strconv.Atoi(s)
+			if err != nil {
+				panic(err)
+			}
+
+			if n > max {
+				max = n
+			}
+
+			crabs[n]++
+		}
+
+		// Loop over all possible options
+		costmin := -1
+		for i := 0; i <= max; i++ {
+			cost := 0
+			for p, n := range crabs {
+				distance := p - i
+				if distance < 0 {
+					distance = -distance
+				}
+
+				cost += cf(distance) * n
+			}
+
+			if cost < costmin || costmin == -1 {
+				costmin = cost
+			}
+		}
+
+		return costmin
+	}
+}
+
+func main() {
+	aoc := aoc.New(2021, 7)
+	
+	aoc.Test(`16,1,2,0,4,2,7,1,2,14`, []int{37, 168})
+
+	aoc.Solution(1, findMinFuel(func (distance int) int {
+		return distance
+	}))
+
+	aoc.Solution(2, findMinFuel(func (distance int) int {
+		return distance * (distance + 1) / 2
+	}))
+}