stack_min.py

# minimum in stack

class Node:
    value = None
    next  = None

    def __init__(self, value, next=None):
        self.value = value
        self.next  = next

class MinStack:

    _min = None
    _int_stack = list()

    def push(self, value):
        if self._min == None:
            self._int_stack.append([value, None])
            self._min = value
        elif self._min != None and value > self._min:
            self._int_stack.append([value, self._min])
        elif self._min != None and value < self._min:
            self._int_stack.append([value, self._min])
            self._min = value


    def pop(self):
        if len(self._int_stack) == 0:
            return None

        last = self._int_stack.pop()
        if(last[0] == self._min):
            self._min = last[1]

        return last[0]


    def minimum(self):
        return self._min


cl = MinStack()
cl.push(3)
cl.push(5)
cl.push(1)
cl.push(9)
cl.push(24)
cl.push(-4)
cl.push(4)

print(99,cl.pop())
print(cl.minimum())
print(99,cl.pop())
print(cl.minimum())
print(99,cl.pop())
print(cl.minimum())
print(99,cl.pop())
print(cl.minimum())
print(99,cl.pop())
print(cl.minimum())
print(99,cl.pop())
print(cl.minimum())