155. Min Stack

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.
题目含义：设计一个最小栈，push, pop, top, 和 getMin 方法都是常量时间

class MinStack {

   private Queue<Integer> p = new LinkedList<>();
    private Integer minValue = Integer.MAX_VALUE;

    /** Initialize your data structure here. */
    public MinStack() {
    }

    public int getMin() {

        for (int i=0;i<p.size();i++)
        {
            Integer value = p.poll();
            minValue = Math.min(minValue,value);
            p.add(value);
        }
        return minValue;
    }

    /** Push element x onto stack. */
    public void push(int x) {
        p.add(x);
        for (int i=1;i<p.size();i++)
        {
            p.add(p.poll());
        }
    }

    /** Removes the element on top of the stack and returns that element. */
    public int pop() {
        return p.poll();
    }

    /** Get the top element. */
    public int top() {
        return p.peek();
    }

    /** Returns whether the stack is empty. */
    public boolean empty() {
        return p.isEmpty();
    }
}