[Swift][우선순위 큐] 백준 1927, 11279 (최소힙, 최대힙)

요구능력

우선순위 큐 (힙)

 

문제풀이

힙과 우선순위 큐의 이론을 알고 생각하면서 따라쳐보시면 이해하기 쉽습니다.

저도 그렇게 익혔습니다.

sortFunction을 <로 할경우 최소힙, >로 할경우 최대힙이됩니다.

 

후기

우선순위큐, 힙에대해 알고있으면 풀리는 간단한문제

 

코드

import Foundation

struct Heap<T: Comparable> {
    private var elements: [T] = []
    private let sortFunction: (T, T) -> Bool
    init (sortFunction: @escaping (T, T) -> Bool){
        self.sortFunction = sortFunction
    }
    var isEmpty: Bool {
        return self.elements.count == 1
    }

    func leftChild(of index: Int) -> Int {
        return index * 2
    }
    func rightChild(of index: Int) -> Int {
        return index * 2 + 1
    }
    func parent(of index: Int) -> Int {
        return (index) / 2
    }
    mutating func diveDown(from index: Int) {
        var higherPriority = index
        let leftIndex = self.leftChild(of: index)
        let rightIndex = self.rightChild(of: index)

        if leftIndex < self.elements.endIndex && self.sortFunction(self.elements[leftIndex], self.elements[higherPriority]) {
            higherPriority = leftIndex
        }
        if rightIndex < self.elements.endIndex && self.sortFunction(self.elements[rightIndex], self.elements[higherPriority]) {
            higherPriority = rightIndex
        }
        if higherPriority != index {
            self.elements.swapAt(higherPriority, index)
            self.diveDown(from: higherPriority)
        }
    }
    mutating func swimUp(from index: Int) {
        var index = index
        while index != 1 && self.sortFunction(self.elements[index], self.elements[self.parent(of: index)]) {
            self.elements.swapAt(index, self.parent(of: index))
            index = self.parent(of: index)
        }
    }
    mutating func insert(node: T) {
        if self.isEmpty {
            self.elements.append(node)
            return
        }
        self.elements.append(node)
        
        self.swimUp(from: self.elements.endIndex - 1)
    }
    mutating func remove() -> T? {
        if self.isEmpty { return nil }
        self.elements.swapAt(1, elements.endIndex - 1)
        let deleted = elements.removeLast()
        self.diveDown(from: 1)

        return deleted
    }
}
var heap = Heap<Int>(sortFunction: <)
heap.insert(node: 0)
var str = ""
let n = Int(String(readLine()!))!
for _ in 0..<n{
    let x = Int(String(readLine()!))!
    if x > 0 {
        heap.insert(node: x)
    }else{
        if let removed = heap.remove() {
            str += "\(removed)\n"
        }else{
            str += "0\n"
        }
    }
}
print(str)