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题目

• 原题连接：155. 最小栈

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1- 思路

思路

• 最小栈 ——> 借助两个栈来实现

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2- 实现

⭐155. 最小栈——题解思路

class MinStack {

    Stack<Integer> data;
    Stack<Integer> min;

    public MinStack() {
        data = new Stack<>();
        min = new Stack<>();
    }

    // 判断当前元素和 min 的peek大小
    public void push(int val) {
        data.push(val);

        if(min.isEmpty() || val<=min.peek()){
            min.push(val);
        }else{
            min.push(min.peek());
        }
    }

    public void pop() {
        data.pop();
        min.pop();
    }

    public int top() {
        return data.peek();
    }

    public int getMin() {
        return min.peek();
    }
}

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3- ACM 实现

public class MinStack {

    Stack<Integer> data;
    Stack<Integer> min;

    public MinStack(){
        data = new Stack<>();
        min = new Stack<>();
    }

    public void push(int val){
        data.push(val);
        if(min.isEmpty() || val<=min.peek()){
            min.push(val);
        }else{
            min.push(min.peek());
        }
    }

    // pop
    public void pop(){
        data.pop();
        min.pop();
    }

    // top()
    public int top(){
        return data.peek();
    }

    // getMin()
    public int getMin(){
        return min.peek();
    }


    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        MinStack minStack = null;

        while (scanner.hasNext()) {
            String command = scanner.next();
            if (command.equals("push")) {
                int value = scanner.nextInt();
                minStack.push(value);
            } else if (command.equals("pop")) {
                minStack.pop();
            } else if(command.equals("MinStack")) {
                minStack = new MinStack();
            }
            else if (command.equals("top")) {
                System.out.println(minStack.top());
            } else if (command.equals("getMin")) {
                System.out.println(minStack.getMin());
            }
        }
        scanner.close();
    }

}

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