Min Stack

Min Stack

问题：

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.

思路：

　　两个栈 一个正常栈，一个用来存储Min值

class MinStack {

    private Stack<Integer> normal = new Stack<Integer>();

    private Stack<Integer> min = new Stack<Integer>();

    

    public void push(int x) {

        if(min.isEmpty() || x <= min.peek())

        {

            min.push(x);

        }

        normal.push(x);

    }



    public void pop() {

        int x = normal.pop();

        if(x == min.peek())

        {

           min.pop(); 

        }

    }



    public int top() {

        return normal.peek();

    }



    public int getMin() {

        return min.peek();

    }

}

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