AoC-Day20-Part1.swift

import UIKit

var input =
"""
1
2
-3
3
-2
0
4
"""

let lines = input.split(whereSeparator: \.isNewline)

struct Point: Equatable, Hashable {
    let value: Int
    var hasMoved = false
}

var points: [Point] = lines.map {
    let val = Int(String($0))!
    return Point(value: val, hasMoved: val == 0)
}

while points.contains(where: { $0.hasMoved == false }) {
    let index = points.firstIndex(where: { $0.hasMoved == false })!
    var point = points.remove(at: index)
    point.hasMoved = true
    
    var newIndex = index + point.value
    
    newIndex = newIndex % points.count
    
    if newIndex < 0 {
        newIndex = points.count + newIndex
    }
    
    if newIndex == 0 {
        newIndex = points.count
    }
    
    points.insert(point, at: newIndex)
}

let values = points.map { $0.value }
let zeroPos = values.firstIndex(of: 0)!

let output = values[(1000 + zeroPos) % values.count] + values[(2000 + zeroPos) % values.count] + values[(3000 + zeroPos) % values.count]
print(output)