Advent Of Code 2024 Day 2

package main

import (
    "bufio"
    "fmt"
    "log"
    "os"
    "slices"
    "strings"
)

func main() {
    puzzleInput := parseFile("input.txt")
    fmt.Println("PartOne: ", partOne(puzzleInput))
    fmt.Println("PartTwo: ", partTwo(puzzleInput))
}

func parseFile(fileName string) [][]int {
    file, err := os.Open("input.txt")
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close()

    scanner := bufio.NewScanner(file)

    reports := make([][]int, 0, 1000)

    for scanner.Scan() {
        fields := strings.Fields(scanner.Text())
        var integerFields []int
        for _, s := range fields {
            integerFields = append(integerFields, stringToInt(s))
        }
        reports = append(reports, integerFields)
    }

    return reports
}

func partOne(reports [][]int) (safeReports int) {
    for _, report := range reports {
        if isValid(report) {
            safeReports++
        }
    }
    return safeReports
}

func partTwo(reports [][]int) (safeReports int) {
    for _, report := range reports {
        if isValid(report) {
            safeReports++
        } else if canBeMadeValid(report) {
            safeReports++
        }
    }
    return safeReports
}

func isValid(report []int) bool {
    isSafe := true

    for i := 1; i < len(report); i++ {
        diff := abs(report[i] - report[i-1])

        if diff > 3 || diff < 1 {
            isSafe = false
        }
    }

    if !isStrictlyIncreasing(report) && !isStrictlyDecreasing(report) {
        isSafe = false
    }

    return isSafe
}

func isStrictlyIncreasing(report []int) bool {
    for i := 1; i < len(report); i++ {
        if report[i-1] >= report[i] {
            return false
        }
    }
    return true
}

func isStrictlyDecreasing(report []int) bool {
    for i := 1; i < len(report); i++ {
        if report[i] >= report[i-1] {
            return false
        }
    }
    return true
}

func canBeMadeValid(report []int) bool {
    for i := range report {
        newSlice := make([]int, len(report))
        copy(newSlice, report)

        slices.Delete(newSlice, i, i+1)
        newSlice = newSlice[:len(newSlice)-1]

        if isValid(newSlice) {
            return true
        }
    }
    return false
}

func abs(a int) int {
    if a < 0 {
        return -1 * a
    }
    return a
}

func stringToInt(str string) (num int) {
    for _, r := range str {
        num *= 10
        num += int(r - '0')
    }

    return num
}