[Swift]LeetCode155. 最小栈 | Min Stack

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Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• getMin() -- Retrieve the minimum element in the stack.

Example:

MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin();   --> Returns -3.
minStack.pop();
minStack.top();      --> Returns 0.
minStack.getMin();   --> Returns -2.

---

设计一个支持 push，pop，top 操作，并能在常数时间内检索到最小元素的栈。

• push(x) -- 将元素 x 推入栈中。
• pop() -- 删除栈顶的元素。
• top() -- 获取栈顶元素。
• getMin() -- 检索栈中的最小元素。

示例:

MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin();   --> 返回 -3.
minStack.pop();
minStack.top();      --> 返回 0.
minStack.getMin();   --> 返回 -2.

---

136ms

class MinStack {
    
    var stack: [Int]
    var minStack: [Int]
    
    /** initialize your data structure here. */
    init() {
        stack = []
        minStack = []
    }
    
    func push(_ x: Int) {
        stack.append(x)
        if minStack.count == 0 {
            minStack.append(x)
        } else {
            minStack.append(min(x, minStack[minStack.count - 1]))
        }
    }
    
    func pop() {
        stack.removeLast()
        minStack.removeLast()
    }
    
    func top() -> Int {
        return stack[stack.count - 1]
    }
    
    func getMin() -> Int {
        return minStack[minStack.count - 1]
    }
}


/**
 * Your MinStack object will be instantiated and called as such:
 * let obj = MinStack()
 * obj.push(x)
 * obj.pop()
 * let ret_3: Int = obj.top()
 * let ret_4: Int = obj.getMin()
 */
 

---

140ms

class MinStack {

    /** initialize your data structure here. */
    var stackArray: [Int]
    var minIndex: Int = 0
    init() {
      stackArray = [Int]()
    }
    
    func push(_ x: Int) {
      stackArray.append(x)
      let currMin = stackArray[minIndex]
      if x < currMin {
          minIndex = stackArray.count - 1
      }
    }
    
    func pop() {
      stackArray.removeLast()
      adjustMinIndex()
    }
    
    func top() -> Int {
      return stackArray.last ?? 0
    }
    
    func getMin() -> Int {
      return stackArray[minIndex]
    }

    func adjustMinIndex() {
        minIndex = 0
        guard stackArray.count > 1 else {return}
        var temp = stackArray[minIndex]
        for i in 1..<stackArray.count {
          if stackArray[i] < temp {
            temp = stackArray[i]
            minIndex = i
          }
        }
    }
}

---

 144ms

class MinStack {
    //需要使用双栈实现
    //保存数据
    var stack: [Int]
    //保存最小值
    var sm: [Int]
    /** initialize your data structure here. */
    init() {
        stack = [Int]()
        sm = [Int]()
    }
    
    func push(_ x: Int) {
        stack.append(x)
        if sm.isEmpty || (!sm.isEmpty && sm.last! >= x)
        {
            sm.append(x)
        }
    }
    
    func pop() {
        if stack.last! == sm.last!
        {
            sm.removeLast()
        }
        stack.removeLast()
    }
    
    func top() -> Int {
        //获取堆栈第一个元素
        return stack.last!
    }
    
    func getMin() -> Int {
        //获取堆栈第一个元素
        return sm.last!
    }
}

/**
 * Your MinStack object will be instantiated and called as such:
 * let obj = MinStack()
 * obj.push(x)
 * obj.pop()
 * let ret_3: Int = obj.top()
 * let ret_4: Int = obj.getMin()
 */
 

---

144ms

class MinStack {

    private var elements: [(val: Int, minUntil: Int)]
    /** initialize your data structure here. */
    init() {
        elements = [(val: Int, minUntil: Int)]()
    }
    
    func push(_ x: Int) {
        if let lastElement = elements.last {
            elements.append((val: x, minUntil: min(lastElement.minUntil, x)))
        } else {
            elements.append((val: x, minUntil: x))
        }
    }
    
    func pop() {
        elements.removeLast()
    }
    
    func top() -> Int {
      return elements.last!.val
    }
    
    func getMin() -> Int {
      return elements.last!.minUntil
    }
}

/**
 * Your MinStack object will be instantiated and called as such:
 * let obj = MinStack()
 * obj.push(x)
 * obj.pop()
 * let ret_3: Int = obj.top()
 * let ret_4: Int = obj.getMin()
 */
 

---

152ms

class MinStack {

    private var stack: [(Int, Int)]

    init() {
        stack = []
    }

    func push(_ x: Int) {
        if stack.isEmpty {
            stack.append((x, x))
        } else {
            let top = stack.last!
            stack.append((x, x < top.1 ? x : top.1))
        }
    }

    func pop() {
        stack.popLast()
    }

    func top() -> Int {
        return stack.last!.0
    }

    func getMin() -> Int {
        return stack.last!.1
    }
}