Shortest substring containing all

shortest_substring.py

def shortest_substring(words, text):
    total, start, mstart, mend = 0, 0, 0, 0
    min_value = len(text)
    counts = defaultdict(int)
    for i in range(len(text)):
        if text[i] in words:
            counts[text[i]] = counts[text[i]] + 1
            if counts[text[i]] == 1:
                total = total + 1
            
            while total == len(words):
                if min_value > i - start:
                    min_value = i - start
                    mstart, mend = start, i
                
                if text[start] in words:
                    counts[text[start]] = counts[text[start]] - 1
                    if counts[text[start]] < 1:
                        total = total - 1
                start = start + 1
                while text[start] not in words:
                    start = start + 1

    return text[mstart: mend + 1] 

print(shortest_substring(set(['a', 'b', 'd']), 'abcefddalmbd'))
print(shortest_substring(set(['a', 'b', 'c']), 'mbalmpdabcl'))
print(shortest_substring(set(['a', 'b', 'c']), 'mbalmpdampzzzbcla'))