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();
    }
}