Advent of Code 2021 Day 3

3a.go

package main

import (
	_ "embed"
	"fmt"
	"strconv"
	"strings"
)

//go:embed input.txt
var input string

func main() {
	lines := strings.Split(input, "\n")
	trueCnts := make([]int, len(lines[0]))
	falseCnts := make([]int, len(lines[0]))

	for _, line := range lines {
		for i, char := range line {
			if char == '0' {
				falseCnts[i]++
			} else if char == '1' {
				trueCnts[i]++
			}
		}
	}

	out1 := ""
	out2 := ""
	for i := 0; i < len(lines[0]); i++ {
		if trueCnts[i] > falseCnts[i] {
			out1 += "1"
			out2 += "0"
		} else {
			out1 += "0"
			out2 += "1"
		}
	}

	num1, err := strconv.ParseInt(out1, 2, 64)
	if err != nil {
		panic(err)
	}
	num2, err := strconv.ParseInt(out2, 2, 64)
	if err != nil {
		panic(err)
	}
	fmt.Println(num1 * num2)
}

3b.go

package main

import (
	_ "embed"
	"fmt"
	"strconv"
	"strings"
)

//go:embed input.txt
var input string

func main() {
	vals := strings.Split(input, "\n")
	var truecnts []int
	var falsecnts []int
	calcstats := func() {
		truecnts = make([]int, len(vals[0]))
		falsecnts = make([]int, len(vals[0]))
		// Calculate stats
		for _, val := range vals {
			for i, char := range val {
				if char == '0' {
					falsecnts[i]++
				} else if char == '1' {
					truecnts[i]++
				}
			}
		}
	}

	// Oxygen rating
	for i := 0; i < len(vals[0]); i++ {
		calcstats()

		// Check
		newVals := make([]string, 0)
		var corrChar byte = ' '
		if falsecnts[i] > truecnts[i] {
			corrChar = '0'
		} else {
			corrChar = '1'
		}

		for _, val := range vals {
			if val[i] == corrChar {
				newVals = append(newVals, val)
			}
		}
		vals = newVals

		if len(vals) == 1 {
			break
		}
	}
	oxygenrating := vals[0]

	// Co2 scrubber rating
	vals = strings.Split(input, "\n")
	for i := 0; i < len(vals[0]); i++ {
		calcstats()

		// Check
		newVals := make([]string, 0)
		var corrChar byte = ' '
		if truecnts[i] < falsecnts[i] {
			corrChar = '1'
		} else {
			corrChar = '0'
		}

		for _, val := range vals {
			if val[i] == corrChar {
				newVals = append(newVals, val)
			}
		}
		vals = newVals

		if len(vals) == 1 {
			break
		}
	}
	corating := vals[0]

	orating, err := strconv.ParseInt(oxygenrating, 2, 64)
	if err != nil {
		panic(err)
	}
	crating, err := strconv.ParseInt(corating, 2, 64)
	if err != nil {
		panic(err)
	}
	fmt.Println(orating * crating)
}