Stack

decompress.py

# Predefined methods
class Stack:
    def __init__(self):
        self.__items = []
        
    def is_empty(self):
        return self.__items == []
    
    def push(self, item):
        self.__items.append(item)
        
    def pop(self):
        if self.is_empty():
            raise IndexError('ERROR: The stack is empty!')
        return self.__items.pop()
    
    def peek(self):
        if self.is_empty():
            raise IndexError('ERROR: The stack is empty!')
        return self.__items[len(self.__items) - 1]
    
    def size(self):
        return len(self.__items)
    
    def __str__(self):
        return 'Stack: ' + str(self.__items)
        
def contains_digit(my_str):
    for c in my_str:
        if c.isdigit():
            return True
    return False


def decompress(comp_str):
    if comp_str == '' or not contains_digit(comp_str):
        return comp_str
    else:
        repeats = Stack()
        for i in range(len(comp_str)):
            if comp_str[i].isdigit():
                if repeats.size() == 0 or repeats.peek()[0] != int(comp_str[i]):
                    repeats.push((int(comp_str[i]), i))
                elif repeats.peek()[0] == int(comp_str[i]):
                    n, start = repeats.pop()
                    return decompress(comp_str[:start] + comp_str[start+1: i] * n + comp_str[i+1:])