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DAY 8 - Advent of Code 2020 w/ GoLang

dizveloper profile image Edvin Updated on ・2 min read

Part 1:
I checked which operation needed to happen and enacted it. I kept a running check to see if an index was revisited. If it was, I broke out of the loop and returned the accumulation.

Part 2:

  1. I looked for the next jmp operation
  2. I changed it to a nop
  3. I reused the code from part1 to return the accumulation, BUT ALSO to return the index at which it terminated
  4. If it terminated before the end of the program, I REVERTED the last changed nop back to jmp and started again on the next jmp NOTE: I followed the running changed index with a global slice to start from in the next recursion.
  5. That recursion continued until I had changed only a single jmp and we reached the end of the program.
package days

import (
    "fmt"
    "strconv"
    "strings"

    inputs "../inputs"
)

// https://adventofcode.com/2020/day/8
// Eight : advent of code, day eight part1 and 2
func Eight() {
    inputSlice := inputs.Day8

    part1(inputSlice)
    part2(inputSlice)
}

func part1(inputSlice []string) {
    acc, _ := oppEvaluator(inputSlice)
    fmt.Print("(Part1) - Accumulator prior to infinite loop restarting: ")
    fmt.Println(acc)
}

var whichOpChanged = []int{0, 0}

func part2(inputSlice []string) {
    innerSlice := inputSlice

    for operation := whichOpChanged[0]; operation < len(innerSlice); operation++ {
        temp := strings.Split(innerSlice[operation], " ")

        typeOfOp := temp[0]
        signedNumber, _ := strconv.Atoi(temp[1])

        if typeOfOp == "nop" && whichOpChanged[0] == operation && whichOpChanged[1] == signedNumber {
            innerSlice[whichOpChanged[0]] = "jmp " + strconv.Itoa(whichOpChanged[1])
        }

        if typeOfOp == "jmp" {
            innerSlice[operation] = "nop " + strconv.Itoa(signedNumber)
            whichOpChanged = []int{operation, signedNumber}
            break
        }
    }

    acc, in := oppEvaluator(innerSlice)
    if in < len(inputSlice) {
        part2(innerSlice)
    } else {
        fmt.Print("(Part2) - Accumulator after termination: ")
        fmt.Println(acc)
    }

}

func oppEvaluator(inputSlice []string) (int, int) {
    accumulator := 0
    operationIndex := 0
    indexVisited := []int{0}

    for {
        temp := strings.Split(inputSlice[operationIndex], " ")

        typeOfOp := temp[0]
        signedNumber, _ := strconv.Atoi(temp[1])

        switch typeOfOp {
        case "acc":
            accumulator = accumulator + signedNumber
            operationIndex++
        case "jmp":
            operationIndex = operationIndex + signedNumber
        case "nop":
            operationIndex++
        default:
            fmt.Println("not an opp")
        }

        if intSliceContains(indexVisited, operationIndex) {
            break
        } else {
            indexVisited = append(indexVisited, operationIndex)
        }

        if operationIndex > len(inputSlice)-1 || operationIndex < 0 {
            break
        }
    }

    return accumulator, operationIndex
}

func intSliceContains(s []int, i int) bool {
    for _, a := range s {
        if a == i {
            return true
        }
    }
    return false
}
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