AdventOfCode.com 2016/Day 3, Part 2 Solution

Day3.playground.swift

import Foundation

//: ## Helpers
func string(fromFile name:String, fileExtension:String) -> String? {
    
    if let filePath = Bundle.main.path(forResource:name, ofType:fileExtension) {
        if let inputData = FileManager.default.contents(atPath: filePath) {
            return String(data: inputData, encoding: .utf8)
        }
    }
    return nil
}


//: ## Solution Objects
struct Triangle {
    let vertices: [Int]
    
    init?(vertices:[Int]) {
        guard vertices.count == 3 else { return nil }
        
        guard vertices[0] + vertices[1] > vertices[2],
            vertices[0] + vertices[2] > vertices[1],
            vertices[2] + vertices[1] > vertices[0] else {
                return nil
        }
        
        self.vertices = vertices
    }
}


//: ## Input Processing
let day = "Day3"

let testInput = "  330  143  338"

func prepareInput() -> [[Int]] {
    if let inputString = string(fromFile: day, fileExtension: "txt") {
        
        let triangleStrings = inputString.components(separatedBy: "\n")                     // Split each line into a string that might represent an array of vertices
        
        return triangleStrings.map { (vertexString) -> [Int] in                             // For each line in the input file...
            return vertexString.components(separatedBy: CharacterSet(charactersIn: " "))    // Split the string into strings by spaces...
                .flatMap({ return Int($0) })                                                // Convert those strings to Ints...
        }
    }
    return [[Int]]()
}

let triangles = prepareInput()

//: ## Solution Execution
var actualTriangles = [Triangle]()

var index = triangles.startIndex
while index < triangles.endIndex {
    
    let endIndex = triangles.index(index, offsetBy: 2)
    guard endIndex < triangles.endIndex else { break }
    
    let triple = triangles[index...endIndex]
    for column in 0...2 {
        if let triangle = Triangle(vertices: triple.map({ return $0[column] })) {
            actualTriangles.append(triangle)
        }
    }
    
    index = triangles.index(index, offsetBy: 3)
}

print("\(actualTriangles.count)")

The swift array indexing could use some work. This is hacky. Need to look at Collection and Sequence protocols for more inspiration!