getMin 使用一个栈

import java.util.Stack;
class getMin{
	Stack<Integer> stack;
	int min;
	public getMin(){
		stack = new Stack<Integer>(); 
		min = Integer.MIN_VALUE;
	}
	public void push(int val){
		if(stack.isEmpty()){
			stack.push(0);
			min = val;
		}
		else{
			int diff = val - min;
			stack.append(diff);
			min = diff>0?min:val;
		}
	}
	public int pop(){
		if(stack.isEmpty()) return -1;
		int diff = stack.pop();
		if(diff < 0){
			top = min;
			min = top - diff;
		}
		else{
			top = min + diff;
		}
		return top;
	}
	public int top(){
		if(stack.peek() < 0){
			return min;
		}
		else{
			return stack.peek() + min;
		}
	}
	public int get_min(){
		if(stack.isEmpty()) return -1;
		return min;
	}

}