alphabet_wars_nuclear_strike.py

"""
Introduction
There is a war and nobody knows - the alphabet war! The letters hide in their nuclear shelters. The nuclear strikes hit
the battlefield and killed a lot of them.

Task
Write a function that accepts battlefield string and returns letters that survived the nuclear strike.

The battlefield string consists of only small letters, #,[ and ].
The nuclear shelter is represented by square brackets []. The letters inside the square brackets represent letters
inside the shelter.
The # means a place where nuclear strike hit the battlefield. If there is at least one # on the battlefield, all
letters outside of shelter die. When there is no any # on the battlefield, all letters survive (but do not expect such
scenario too often ;-P ).
The shelters have some durability. When 2 or more # hit close to the shelter, the shelter is destroyed and all letters
inside evaporate. The 'close to the shelter' means on the ground between the shelter and the next shelter (or
beginning/end of battlefield). The below samples make it clear for you.

Example
abde[fgh]ijk     => "abdefghijk"  (all letters survive because there is no # )
ab#de[fgh]ijk    => "fgh" (all letters outside die because there is a # )
ab#de[fgh]ij#k   => ""  (all letters dies, there are 2 # close to the shellter )
##abde[fgh]ijk   => ""  (all letters dies, there are 2 # close to the shellter )
##abde[fgh]ijk[mn]op => "mn" (letters from the second shelter survive, there is no # close)
#ab#de[fgh]ijk[mn]op => "mn" (letters from the second shelter survive, there is no # close)
#abde[fgh]i#jk[mn]op => "mn" (letters from the second shelter survive, there is only 1 # close)
[a]#[b]#[c]  => "ac"
[a]#b#[c][d] => "d"
[a][b][c]    => "abc"
##a[a]b[c]#  => "c"

"""

import re


def alphabet_war(battlefield):
    if '#' not in battlefield:
        return battlefield.replace('[', '').replace(']', '')
    shelter_arr = []
    strike_num = 0
    shelter_str = ''
    shelter_flag = False
    for idx, char in enumerate(battlefield):
        if char == '#':
            strike_num += 1
        elif char == '[':
            shelter_arr.append(strike_num)
            strike_num = 0
            shelter_flag = True
            shelter_str = ''
        elif char == ']':
            shelter_arr.append(shelter_str)
            shelter_flag = False
        else:
            if shelter_flag:
                shelter_str += char
    shelter_arr.append(strike_num)
    return ''.join(item for idx, item in enumerate(shelter_arr) if
                   type(item) == str and shelter_arr[idx - 1] + shelter_arr[idx + 1] < 2)