Advent of Code — Day 12 — Javascript

For day 12, you are given a set of direction and and you need to maintain the X and Y position from the origin. It also asks you to keep track of the direction that you are facing. Initially, you are facing east and will be turning in increments of 90 degrees to face a different direction.

N - Move north x units
S - Move south x units
E - Move east x units
W - Move west x units
L - Turn left y degrees
R - Turn right y degrees
F - Move forward based on direction facing

If it does not make sense yet, let’s take a look at the sample and do a simple walkthrough.

Initial Direction = [0, 0] and facing East
F10 - Forward 10
[10, 0] and facing East
N3
[10, 3] and facing East
F7
[17, 3] and facing East
R90
[17, 3] and facing South 
F11
[17, -8]

The value that Advent of Code asks for is the sum of the absolute value of the x and y value: 17 + 8 = 25

We start the program as we always do with splitting the directions by newline characters. We will need two variables to keep track of the x and y axis. We also need a variable to keep track of the direction that we are facing.

function day12(input){
    let xAxis = 0
    let yAxis = 0
    //[North, East, South, West]
    let facing = 1
    let directions = input.split('\n')
}

We will be iterating through each set of directions and using the first letter to decide which function we will be performing. Each direction follows a pattern of a letter instruction followed by a number.

function day12(input){
    let xAxis = 0
    let yAxis = 0
    //[North, East, South, West]
    let facing = 1
    let directions = input.split('\n')
    for(let i = 0; i < directions.length; i++){
        let instr = directions[i]
        letter letter = instr[0]
        let num = parseInt(instr.slice(1, instr.length))
    }
}

The number in each instruction can be multiple digits which means that we cannot use a split on the whole thing.

function day12(input){
    let xAxis = 0
    let yAxis = 0
    //[North, East, South, West]
    let facing = 1
    let directions = input.split('\n')
    for(let i = 0; i < directions.length; i++){
        let instr = directions[i]
        letter letter = instr[0]
        let num = parseInt(instr.slice(1, instr.length))
        if(instr === "N") 
            yAxis += num
        if(instr === "N") 
            yAxis += num
        if(instr === "N") 
            yAxis += num
        if(instr === "N") 
            yAxis += num
    }
}

We have taken care of the X and Y positioning with this.

The left and right turning is given in increments of 90. When turning left and right

function day12(input){
    let xAxis = 0
    let yAxis = 0
    //[North, East, South, West]
    let facing = 1
    let directions = input.split('\n')
    for(let i = 0; i < directions.length; i++){
        let instr = directions[i]
        let letter = instr[0]
        let num = parseInt(instr.slice(1, instr.length))
        if(instr === "N") 
            yAxis += num
        if(instr === "N") 
            yAxis += num
        if(instr === "N") 
            yAxis += num
        if(instr === "N") 
            yAxis += num
//[North, East, South, West] //Starts East
        if(instr === "L"){
            facing -= (num / 90) 
            //L90 = Facing - 1 
            //L180 = Facing - 2
            facing %= 4
        }
        if(instr === "R"){
            facing += (num / 90)
            facing %= 4
        }
        if(instr === "F" && facing === 0)
            yAxis += num 
        if(instr === "F" && facing === 1)
            xAxis += num
        if(instr === "F" && facing === 2)
            yAxis -= num
        if(instr === "F" && facing === 3)
            xAxis -= num
    }
    return Math.abs(xAxis) + Math.abs(yAxis)
}