mycode/code_study/Baekjoon/swift/1238.swift

// 그냥 큐를 써도 통과가 되긴 하다만 연습삼아서 우선순위큐를 직접 구현해서 풀어봄
struct PriorityQueue {
    private var heap: [(now: Int, time: Int)] = []

    public var isEmpty: Bool {
        return heap.isEmpty
    }

    public var count: Int {
        return heap.count
    }

    public func peek() -> (now: Int, time: Int)? {
        return heap.first
    }

    public mutating func enqueue(_ element: (now: Int, time: Int)) {
        heap.append(element)
        siftUp(from: heap.count - 1)
    }

    public mutating func dequeue() -> (now: Int, time: Int)? {
        guard !heap.isEmpty else { return nil }
        if heap.count == 1 {
            return heap.removeLast()
        }
        
        heap.swapAt(0, heap.count - 1)
        let dequeuedElement = heap.removeLast()
        siftDown(from: 0)
        
        return dequeuedElement
    }

    private func parentIndex(of i: Int) -> Int { (i - 1) / 2 }
    private func leftChildIndex(of i: Int) -> Int { 2 * i + 1 }
    private func rightChildIndex(of i: Int) -> Int { 2 * i + 2 }

    private mutating func siftUp(from index: Int) {
        var childIndex = index
        var parentIndex = self.parentIndex(of: childIndex)

        while childIndex > 0 && heap[childIndex].time < heap[parentIndex].time {
            heap.swapAt(childIndex, parentIndex)
            childIndex = parentIndex
            parentIndex = self.parentIndex(of: childIndex)
        }
    }

    private mutating func siftDown(from index: Int) {
        var parentIndex = index
        
        while true {
            let leftIndex = leftChildIndex(of: parentIndex)
            let rightIndex = rightChildIndex(of: parentIndex)
            var smallestIndex = parentIndex

            if leftIndex < heap.count && heap[leftIndex].time < heap[smallestIndex].time {
                smallestIndex = leftIndex
            }

            if rightIndex < heap.count && heap[rightIndex].time < heap[smallestIndex].time {
                smallestIndex = rightIndex
            }

            if smallestIndex == parentIndex {
                return
            }

            heap.swapAt(parentIndex, smallestIndex)
            parentIndex = smallestIndex
        }
    }
}

if let input = readLine(),
   let nums = input.split(separator: " ").compactMap({Int($0)}) as? [Int],
   nums.count == 3
{
    let N = nums[0]
    let M = nums[1]
    let X = nums[2]
    
    var graph: [[(now: Int, time: Int)]] = Array(repeating: [], count: N+1)
    var reverse_graph: [[(now: Int, time: Int)]] = Array(repeating: [], count: N+1)
    
    for _ in 0..<M {
        if let line = readLine(),
           let info = line.split(separator: " ").compactMap({Int($0)}) as? [Int],
           info.count == 3
        {
            let u = info[0]
            let v = info[1]
            let t = info[2]
            
            graph[u].append((now: v, time: t))
            reverse_graph[v].append((now: u, time: t))
        }
    }
    
    var gotime = Array(repeating: Int.max, count: N+1) // N -> X
    var comingtime = Array(repeating: Int.max, count: N+1) // X -> N
    
    var pq = PriorityQueue()
    pq.enqueue((now: X, time: 0))
    comingtime[X] = 0
    
    while !pq.isEmpty {
        if let current = pq.dequeue() {
            if comingtime[current.now] < current.time {
                continue
            }
            
            for i in 0..<reverse_graph[current.now].count {
                if comingtime[reverse_graph[current.now][i].now] > current.time + reverse_graph[current.now][i].time {
                    comingtime[reverse_graph[current.now][i].now] = current.time + reverse_graph[current.now][i].time
                    pq.enqueue((now: reverse_graph[current.now][i].now, time: current.time + reverse_graph[current.now][i].time))
                }
            }
        }
    }
    
    pq.enqueue((now: X, time: 0))
    gotime[X] = 0
    while !pq.isEmpty {
        if let current = pq.dequeue() {
            if gotime[current.now] < current.time {
                continue
            }
            
            for i in 0..<graph[current.now].count {
                if gotime[graph[current.now][i].now] > current.time + graph[current.now][i].time {
                    gotime[graph[current.now][i].now] = current.time + graph[current.now][i].time
                    pq.enqueue((now: graph[current.now][i].now, time: current.time + graph[current.now][i].time))
                }
            }
        }
    }
    
    var maxTime = 0;
    for n in 1...N {
        maxTime = max(maxTime, comingtime[n] + gotime[n])
    }
    
    print(maxTime)
}