[Swift]LeetCode1167. 连接棒材的最低费用 | Minimum Cost to Connect Sticks

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You have some sticks with positive integer lengths.

You can connect any two sticks of lengths X and Y into one stick by paying a cost of X + Y.  You perform this action until there is one stick remaining.

Return the minimum cost of connecting all the given sticks into one stick in this way.

 

Example 1:

Input: sticks = [2,4,3]
Output: 14

Example 2:

Input: sticks = [1,8,3,5]
Output: 30

 

Constraints:

• 1 <= sticks.length <= 10^4
• 1 <= sticks[i] <= 10^4

---

为了装修新房，你需要加工一些长度为正整数的棒材 sticks。

如果要将长度分别为 X 和 Y 的两根棒材连接在一起，你需要支付 X + Y 的费用。 由于施工需要，你必须将所有棒材连接成一根。

返回你把所有棒材 sticks 连成一根所需要的最低费用。注意你可以任意选择棒材连接的顺序。

 

示例 1：

输入：sticks = [2,4,3]
输出：14
解释：先将 2 和 3 连接成 5，花费 5；再将 5 和 4 连接成 9；总花费为 14。

示例 2：

输入：sticks = [1,8,3,5]
输出：30

 

提示：

• 1 <= sticks.length <= 10^4
• 1 <= sticks[i] <= 10^4

---

1884 ms

class Solution {
    func connectSticks(_ sticks: [Int]) -> Int {
        var pq:PriorityQueue<Int> = PriorityQueue<Int> { $0 < $1 }
        for v in sticks
        {
            pq.push(v)
        }
        var ans:Int = 0
        while(pq.count > 1)
        {
            let x:Int = pq.pop()!
            let y:Int = pq.pop()!
            let sum:Int = x + y
            ans += sum
            pq.push(sum)            
        }
        return ans
    }
}

public struct PriorityQueue<T> {
  fileprivate var heap: Heap<T>
  public init(sort: @escaping (T, T) -> Bool) {
    heap = Heap(sort: sort)
  }

  public var isEmpty: Bool {
    return heap.isEmpty
  }

  public var count: Int {
    return heap.count
  }

  public func peek() -> T? {
    return heap.peek()
  }

  public mutating func push(_ element: T) {
    heap.insert(element)
  }

  public mutating func pop() -> T? {
    return heap.remove()
  }

  public mutating func changePriority(index i: Int, value: T) {
    return heap.replace(index: i, value: value)
  }
}

extension PriorityQueue where T: Equatable {
  public func index(of element: T) -> Int? {
    return heap.index(of: element)
  }
}

public struct Heap<T> {
  var nodes = [T]()

  private var orderCriteria: (T, T) -> Bool

  public init(sort: @escaping (T, T) -> Bool) {
    self.orderCriteria = sort
  }
  
  public init(array: [T], sort: @escaping (T, T) -> Bool) {
    self.orderCriteria = sort
    configureHeap(from: array)
  }

  private mutating func configureHeap(from array: [T]) {
    nodes = array
    for i in stride(from: (nodes.count/2-1), through: 0, by: -1) {
      shiftDown(i)
    }
  }
  
  public var isEmpty: Bool {
    return nodes.isEmpty
  }
  
  public var count: Int {
    return nodes.count
  }

  @inline(__always) internal func parentIndex(ofIndex i: Int) -> Int {
    return (i - 1) / 2
  }

  @inline(__always) internal func leftChildIndex(ofIndex i: Int) -> Int {
    return 2*i + 1
  }

  @inline(__always) internal func rightChildIndex(ofIndex i: Int) -> Int {
    return 2*i + 2
  }
  
  public func peek() -> T? {
    return nodes.first
  }
  
  public mutating func insert(_ value: T) {
    nodes.append(value)
    shiftUp(nodes.count - 1)
  }
  
  public mutating func insert<S: Sequence>(_ sequence: S) where S.Iterator.Element == T {
    for value in sequence {
      insert(value)
    }
  }
  
  public mutating func replace(index i: Int, value: T) {
    guard i < nodes.count else { return }
    
    remove(at: i)
    insert(value)
  }

  @discardableResult public mutating func remove() -> T? {
    guard !nodes.isEmpty else { return nil }
    
    if nodes.count == 1 {
      return nodes.removeLast()
    } else {
      let value = nodes[0]
      nodes[0] = nodes.removeLast()
      shiftDown(0)
      return value
    }
  }
  
  @discardableResult public mutating func remove(at index: Int) -> T? {
    guard index < nodes.count else { return nil }
    
    let size = nodes.count - 1
    if index != size {
      nodes.swapAt(index, size)
      shiftDown(from: index, until: size)
      shiftUp(index)
    }
    return nodes.removeLast()
  }

  internal mutating func shiftUp(_ index: Int) {
    var childIndex = index
    let child = nodes[childIndex]
    var parentIndex = self.parentIndex(ofIndex: childIndex)
    
    while childIndex > 0 && orderCriteria(child, nodes[parentIndex]) {
      nodes[childIndex] = nodes[parentIndex]
      childIndex = parentIndex
      parentIndex = self.parentIndex(ofIndex: childIndex)
    }
    
    nodes[childIndex] = child
  }

  internal mutating func shiftDown(from index: Int, until endIndex: Int) {
    let leftChildIndex = self.leftChildIndex(ofIndex: index)
    let rightChildIndex = leftChildIndex + 1

    var first = index
    if leftChildIndex < endIndex && orderCriteria(nodes[leftChildIndex], nodes[first]) {
      first = leftChildIndex
    }
    if rightChildIndex < endIndex && orderCriteria(nodes[rightChildIndex], nodes[first]) {
      first = rightChildIndex
    }
    if first == index { return }
    
    nodes.swapAt(index, first)
    shiftDown(from: first, until: endIndex)
  }
  
  internal mutating func shiftDown(_ index: Int) {
    shiftDown(from: index, until: nodes.count)
  }
  
}

extension Heap where T: Equatable {
    
    public func index(of node: T) -> Int? {
        return nodes.firstIndex(where: { $0 == node })
    }
    
    @discardableResult public mutating func remove(node: T) -> T? {
        if let index = index(of: node) {
            return remove(at: index)
        }
        return nil
    }
}