栈的判断，入出取

class SeqStack(object):
    def __init__(self,max):
        self.max = max
        self.top = -1
        self.stack = [None for i in range(self.max)]
        
    def empty(self):
        return self.top is -1

    def push(self,val):
        if self.top == self.max -1:
            raise IndexError("zym")
        else:
            self.top += 1
            self.stack[self.top] = val

    def pop(self):
        if self.empty():
            raise IndexError("zwk")
        else:
            cur = self.stack[self.top]
            self.top -= 1
            return cur

    def peak(self):
        if self.empty():
            raise IndexError("zwk")
        else:
            return self.stack[self.top]

if __name__ == "__main__":
    s = SeqStack(8)
    for i in range(0,5):
        s.push(i)
    print(s.peak())
    s.pop()
    print(s.peak())
    s.push(8)
    s.push(9)
            

4
3

class Node(object):
    def __init__(self,val):
        self.val = val
        self.next = None

class LinkedStack(object):
    def __init__(self):
        self.top = None

    def empty(self):
        return self.top is None
    
    def push(self,val):
        newNode = Node(val)
        newNode.next = self.top
        self.top  = newNode
        
    def pop(self):
        if self.empty():
            raise IndexError("zwk")
        else:
            temp = self.top
            self.top = self.top.next
            return temp

    def peak(self):
        if self.empty():
            raise IndexError("zwk")
        else:
            return self.top.val

if __name__ == "__main__":
    s = LinkedStack()
    for i in range(1,5):
        s.push(i)
    print(s.peak())
    s.pop()
    print(s.peak())

4
3