feat: add swift implementation to lcof problem: No.41 (doocs#2922)

Author: klever34

lcof/面试题41. 数据流中的中位数/README.md

@@ -412,6 +412,123 @@ public class MedianFinder {
  */
 ```
 
+#### Swift
+
+```swift
+class MedianFinder {
+    private var lowerHalf = Heap<Int>(sort: >)
+    private var upperHalf = Heap<Int>(sort: <)
+
+    init() {}
+
+    func addNum(_ num: Int) {
+        if lowerHalf.count == 0 || num <= lowerHalf.peek()! {
+            lowerHalf.insert(num)
+        } else {
+            upperHalf.insert(num)
+        }
+
+        if lowerHalf.count > upperHalf.count + 1 {
+            upperHalf.insert(lowerHalf.remove()!)
+        } else if upperHalf.count > lowerHalf.count {
+            lowerHalf.insert(upperHalf.remove()!)
+        }
+    }
+
+    func findMedian() -> Double {
+        if lowerHalf.count > upperHalf.count {
+            return Double(lowerHalf.peek()!)
+        } else {
+            return (Double(lowerHalf.peek()!) + Double(upperHalf.peek()!)) / 2.0
+        }
+    }
+}
+
+struct Heap<T> {
+    var elements: [T]
+    let sort: (T, T) -> Bool
+
+    init(sort: @escaping (T, T) -> Bool) {
+        self.sort = sort
+        self.elements = []
+    }
+
+    var count: Int {
+        return elements.count
+    }
+
+    func peek() -> T? {
+        return elements.first
+    }
+
+    mutating func insert(_ value: T) {
+        elements.append(value)
+        siftUp(from: elements.count - 1)
+    }
+
+    mutating func remove() -> T? {
+        guard !elements.isEmpty else { return nil }
+        if elements.count == 1 {
+            return elements.removeLast()
+        } else {
+            let value = elements[0]
+            elements[0] = elements.removeLast()
+            siftDown(from: 0)
+            return value
+        }
+    }
+
+    private mutating func siftUp(from index: Int) {
+        var child = index
+        var parent = parentIndex(of: child)
+        while child > 0 && sort(elements[child], elements[parent]) {
+            elements.swapAt(child, parent)
+            child = parent
+            parent = self.parentIndex(of: child)
+        }
+    }
+
+    private mutating func siftDown(from index: Int) {
+        var parent = index
+        while true {
+            let left = leftChildIndex(of: parent)
+            let right = rightChildIndex(of: parent)
+            var candidate = parent
+            if left < elements.count && sort(elements[left], elements[candidate]) {
+                candidate = left
+            }
+            if right < elements.count && sort(elements[right], elements[candidate]) {
+                candidate = right
+            }
+            if candidate == parent {
+                return
+            }
+            elements.swapAt(parent, candidate)
+            parent = candidate
+        }
+    }
+
+    private func parentIndex(of index: Int) -> Int {
+        return (index - 1) / 2
+    }
+
+    private func leftChildIndex(of index: Int) -> Int {
+        return 2 * index + 1
+    }
+
+    private func rightChildIndex(of index: Int) -> Int {
+        return 2 * index + 2
+    }
+}
+
+/**
+ * Your MedianFinder object will be instantiated and called as such:
+ * let obj = MedianFinder();
+ * obj.addNum(num);
+ * let param_2 = obj.findMedian();
+ */
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题41. 数据流中的中位数/Solution.swift

@@ -0,0 +1,112 @@
+class MedianFinder {
+    private var lowerHalf = Heap<Int>(sort: >)
+    private var upperHalf = Heap<Int>(sort: <)
+
+    init() {}
+
+    func addNum(_ num: Int) {
+        if lowerHalf.count == 0 || num <= lowerHalf.peek()! {
+            lowerHalf.insert(num)
+        } else {
+            upperHalf.insert(num)
+        }
+
+        if lowerHalf.count > upperHalf.count + 1 {
+            upperHalf.insert(lowerHalf.remove()!)
+        } else if upperHalf.count > lowerHalf.count {
+            lowerHalf.insert(upperHalf.remove()!)
+        }
+    }
+
+    func findMedian() -> Double {
+        if lowerHalf.count > upperHalf.count {
+            return Double(lowerHalf.peek()!)
+        } else {
+            return (Double(lowerHalf.peek()!) + Double(upperHalf.peek()!)) / 2.0
+        }
+    }
+}
+
+struct Heap<T> {
+    var elements: [T]
+    let sort: (T, T) -> Bool
+
+    init(sort: @escaping (T, T) -> Bool) {
+        self.sort = sort
+        self.elements = []
+    }
+
+    var count: Int {
+        return elements.count
+    }
+
+    func peek() -> T? {
+        return elements.first
+    }
+
+    mutating func insert(_ value: T) {
+        elements.append(value)
+        siftUp(from: elements.count - 1)
+    }
+
+    mutating func remove() -> T? {
+        guard !elements.isEmpty else { return nil }
+        if elements.count == 1 {
+            return elements.removeLast()
+        } else {
+            let value = elements[0]
+            elements[0] = elements.removeLast()
+            siftDown(from: 0)
+            return value
+        }
+    }
+
+    private mutating func siftUp(from index: Int) {
+        var child = index
+        var parent = parentIndex(of: child)
+        while child > 0 && sort(elements[child], elements[parent]) {
+            elements.swapAt(child, parent)
+            child = parent
+            parent = self.parentIndex(of: child)
+        }
+    }
+
+    private mutating func siftDown(from index: Int) {
+        var parent = index
+        while true {
+            let left = leftChildIndex(of: parent)
+            let right = rightChildIndex(of: parent)
+            var candidate = parent
+            if left < elements.count && sort(elements[left], elements[candidate]) {
+                candidate = left
+            }
+            if right < elements.count && sort(elements[right], elements[candidate]) {
+                candidate = right
+            }
+            if candidate == parent {
+                return
+            }
+            elements.swapAt(parent, candidate)
+            parent = candidate
+        }
+    }
+
+    private func parentIndex(of index: Int) -> Int {
+        return (index - 1) / 2
+    }
+
+    private func leftChildIndex(of index: Int) -> Int {
+        return 2 * index + 1
+    }
+
+    private func rightChildIndex(of index: Int) -> Int {
+        return 2 * index + 2
+    }
+}
+
+/**
+ * Your MedianFinder object will be instantiated and called as such:
+ * let obj = MedianFinder();
+ * obj.addNum(num);
+ * let param_2 = obj.findMedian();
+ */