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.
• 代码如下：
• class MinStack {
      private Stack<Integer>stack =new Stack<Integer>();
      private Stack<Integer>minstack=new Stack<Integer>();
      public void push(int x) {
          if(minstack.isEmpty()||x<=minstack.peek())
          minstack.push(x);
          stack.push(x);
      }
     public void pop() {
          if(stack.peek().equals(minstack.peek()))
          minstack.pop();
          stack.pop();
      }
      public int top() {
           return stack.peek(); 
      }
      public int getMin() {
          return minstack.peek(); 
      }
  }
  
• 参考博文：http://blog.csdn.net/ljiabin/article/details/40982153