DijkstraPath.swift

struct Path: Comparable {
    let cumulativeWeight: Int
    let lastNode: Node
    let previousPath: Path?
  
    init(toNode: Node, viaConnection: Connection?=nil, viaPath: Path?=nil) {
        if let
            previousPath = viaPath,
            lastConnection = viaConnection {
                self.cumulativeWeight = lastConnection.weight + previousPath.cumulativeWeight
        } else {
            self.cumulativeWeight = 0
        }
    
        self.lastNode = toNode
        self.previousPath = viaPath
    }
}

func ==(x: Path, y: Path) -> Bool {
    return x.cumulativeWeight == y.cumulativeWeight
}

func <(x: Path, y: Path) -> Bool {
    return x.cumulativeWeight < y.cumulativeWeight
}