2021 - Day 3 (Improved implementation)

2021/3/improved.go

@@ -0,0 +1,154 @@
+package main
+
+import (
+	aoc "AoC/2021/common"
+	"bufio"
+	"log"
+	"strconv"
+)
+
+func main() {
+	part1()
+	part2()
+}
+
+func count(entries []string, width int) [2][]int {
+	counts := [2][]int{make([]int, width), make([]int, width)}
+
+	for _, entry := range entries {
+		for i, c := range entry {
+			if string(c) == "0" {
+				counts[0][i]++
+			} else if string(c) == "1" {
+				counts[1][i]++
+			} else {
+				log.Fatalf("Unknown character '%s'\n", string(c))
+			}
+		}
+	}
+
+	return counts
+}
+
+func filter(entries []string, i int, value string) []string {
+	n := 0
+	for _, num := range entries {
+		if string(num[i]) == value {
+			entries[n] = num
+			n++
+		}
+	}
+
+	return entries[:n]
+}
+
+func process(input *bufio.Scanner) ([]string, int) {
+	var numbers []string
+	width := 0
+
+	for i :=0; input.Scan(); i++ {
+		line := input.Text()
+		numbers = append(numbers, line)
+
+		if len(line) > width {
+			width  = len(line)
+		}
+	}
+
+	return numbers, width
+}
+
+func part1() {
+	aoc := aoc.New(2021, 3)
+
+	aoc.Test(`
+00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010
+	`, 198)
+
+	aoc.Solution(func (input *bufio.Scanner) int {
+		entries, width := process(input)
+		counts := count(entries, width)
+
+		gamma := 0
+		epsilon := 0
+		for i := 0; i < width; i++ {
+			if counts[0][i] > counts[1][i] {
+				epsilon += 1 << (width - 1 - i)
+			} else {
+				gamma += 1 << (width - 1 - i)
+			}
+		}
+
+		return gamma * epsilon
+	})
+}
+
+func part2() {
+	aoc := aoc.New(2021, 3)
+
+	aoc.Test(`
+00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010
+	`, 230)
+
+	aoc.Solution(func (input *bufio.Scanner) int {
+		oxygen, width := process(input)
+		oxygenCounts := count(oxygen, width)
+
+		co2 := make([]string, len(oxygen)); copy(co2, oxygen)
+		co2Counts := count(co2, width)
+
+		for i := 0; i < width; i++ {
+			f1 := "1"
+			if oxygenCounts[0][i] > oxygenCounts[1][i] {
+				f1 = "0"
+			}
+			if len(oxygen) > 1 {
+				oxygen = filter(oxygen, i, f1)
+				oxygenCounts = count(oxygen, width)
+			}
+
+			f2 := "0"
+			if co2Counts[0][i] > co2Counts[1][i] {
+				f2 = "1"
+			}
+			if len(co2) > 1 {
+				co2 = filter(co2, i, f2)
+				co2Counts = count(co2, width)
+			}
+		}
+
+		oxygenNum, err := strconv.ParseInt(oxygen[0], 2, 0)
+		if err != nil {
+			panic(err)
+		}
+
+		co2Num, err := strconv.ParseInt(co2[0], 2, 0)
+		if err != nil {
+			panic(err)
+		}
+
+		return int(oxygenNum) * int(co2Num)
+	})
+}