countdown.py

# you'll need a .txt file of english words.
# you can find one here https://github.com/dwyl/english-words/blob/master/words_alpha.txt
# inspiration 8 out of 10 cats does countdown https://youtu.be/l9MXCjPwDro 

from enum import Enum, auto

SYMBOL = "+*-/"
cache = set()

def symbol(arr, target, path):
    arr.sort()
    key = str(arr)+str(target)
    if key in cache:
        return None
    cache.add(key)
    if target in arr:
        return path
    if len(arr) <= 1:
        return None
    for sym in SYMBOL:
        tmp = item(arr, target, sym, path+"\n")
        if tmp is not None:
            return tmp

def op(sym,a,b):
    if sym == "+":
        return a+b
    if sym == "-":
        return a-b
    if sym == "*":
        return a*b
    if sym == "/":
        if b == 0:
            return None
        return a/b
    raise Exception('Error occured at {function} with {p1,p2,p3}'.format(function='op',p1=sym,p2=a,p3=b))

def item(arr, target, sym, path):
    if target in arr:
        return path
    if len(arr) <= 1:
        return None
    n = len(arr)
    for i in range(n):
        ith = arr[i]
        for j in range(n):
            if i == j:
                continue
            jth = arr[j]
            val = op(sym,ith,jth)
            if val is None:
                continue
            newArr = [arr[k] for k in range(n) if not (k==j or k==i)]
            newArr.append(val)
            tmp = symbol(newArr, target, '{} {} {} {} = {}'.format(path,ith,sym,jth,val))
            if tmp is not None:
                return tmp

def countdown(arr, target):
    cache.clear()
    print(symbol(arr, target, ""))

english = open("english_words.txt", "r").readlines()
english = [i.strip().lower() for i in english]
english_words = dict()
for word in english:
    key = ''.join(sorted(word))
    if key not in english_words:
        english_words[key] = [word]
    else:
        english_words[key].append(word)

def countdown_word(letters):
    q = [letters]
    while len(q) != 0:
        word = q.pop(0)
        word = ''.join(sorted(word))
        if word in english_words:
            return english_words[word]
        for i in range(len(word)):
            q.append(word[:i] + word[i+1:])
    return ""

countdown([10,5,1], 3)
countdown([100,4,5,4,7,10], 579)
countdown_word("iwadshong")