155.java

class MinStack {
    Stack<Long> stack;
    long min;
    /** initialize your data structure here. */
    public MinStack() {
        stack = new Stack<>();   
    }
    
    public void push(int x) {
        if(stack.isEmpty()){
            stack.push(0L);
            min=x;
        }else{
            stack.push(x-min);
            if(x<min) min=x;
        }
    }
    
    public void pop() {
        if (stack.isEmpty()) return;
        long pop=stack.pop();
        if (pop<0)  min=min-pop;
    }
    
    public int top() {
        long top=stack.peek();
        if (top>0){
            return (int)(top+min);
        }else{
           return (int)(min);
        }
    }
    
    public int getMin() {
        return (int)min;
    }
}

/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack obj = new MinStack();
 * obj.push(x);
 * obj.pop();
 * int param_3 = obj.top();
 * int param_4 = obj.getMin();
 */