3.2---最小栈

//思路：入栈时不是最小值，永远都没机会成为最小值。

import java.util.Stack;
class MinStack {

    private Stack<Integer> stack = new Stack<Integer>();
    private Stack<Integer> minStack = new Stack<Integer>();
	
    public void push(int x) {
		stack.push(x);
		if(!minStack.empty())
		{
			int min = minStack.peek();
			if(x <= min)
			{
				minStack.push(x);
			}
		}
		else
		{
			minStack.push(x);
		}
    }

    public void pop() {
        
    	if(minStack.size() != 0 && ((int)stack.peek() == (int)minStack.peek()))
        {
        	minStack.pop();
     
        }
    	stack.pop();
    }

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

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