Leetcode155最小栈

设计一个支持 push，pop，top 操作，并能在常数时间内检索到最小元素的栈。

• push(x) -- 将元素 x 推入栈中。
• pop() -- 删除栈顶的元素。
• top() -- 获取栈顶元素。
• getMin() -- 检索栈中的最小元素。

示例:

MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin();   --> 返回 -3.
minStack.pop();
minStack.top();      --> 返回 0.
minStack.getMin();   --> 返回 -2.

class MinStack {

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