Create 0239-sliding-window-maximum.swift

Author: drxlx

swift/0239-sliding-window-maximum.swift

@@ -0,0 +1,105 @@
+/**
+ * Question Link: https://leetcode.com/problems/sliding-window-maximum/
+ */
+
+ class SlidingWindowMaximum {
+    func maxSlidingWindow(_ nums: [Int], _ k: Int) -> [Int] {
+        var output = [Int]()
+        var deque = Deque()
+        var l = 0
+        var r = 0
+
+        while r < nums.count {
+            while !deque.isEmpty && nums[deque.last!] < nums[r] {
+                deque.popRight()
+            }
+            deque.pushRight(r)
+
+            if l > deque.first! {
+                deque.popLeft()
+            }
+
+            if (r + 1) >= k {
+                output.append(nums[deque.first!])
+                l += 1
+            }
+
+            r += 1
+        }
+
+        return output
+    }
+}
+
+struct Deque {
+    private var storage: [Int?]
+    private var head: Int
+    private var capacity: Int
+    private let originalCapacity: Int
+
+    var isEmpty: Bool {
+        storage.count - head == 0
+    }
+
+    var first: Int? {
+        if isEmpty {
+            return nil
+        } else {
+            return storage[head]
+        }
+    }
+
+    var last: Int? {
+        if isEmpty {
+            return nil
+        } else {
+            return storage.last!
+        }
+    }
+
+    init(capacity: Int = 10) {
+        self.capacity = max(capacity, 1)
+        self.storage = [Int?](repeating: nil, count: capacity)
+        self.originalCapacity = self.capacity
+        self.head = capacity
+    }
+
+    mutating func pushLeft(_ value: Int) {
+        if head == 0 {
+            capacity *= 2
+            let emptySpace = [Int?](repeating: nil, count: capacity)
+            storage.insert(contentsOf: emptySpace, at: 0)
+            head = capacity
+        }
+
+        head -= 1
+        storage[head] = value
+    }
+
+    mutating func popLeft() {
+        guard
+            head < storage.count,
+            let value = storage[head]
+        else {
+            return
+        }
+
+        storage[head] = nil
+        head += 1
+
+        if capacity >= originalCapacity, head >= capacity * 2 {
+            let emptySpace = capacity + capacity / 2
+            storage.removeFirst(emptySpace)
+            head -= emptySpace
+            capacity /= 2
+        }
+    }
+
+    mutating func pushRight(_ value: Int) {
+        storage.append(value)
+    }
+
+    mutating func popRight() {
+        storage.removeLast()
+    }
+}