def min_window(str1, str2):
    # save the size of str1 and str2
    size_str1, size_str2 = len(str1), len(str2)

    # initialize min_sub_len to a very large number (infinity)
    min_sub_len = float('inf')

    # initialize pointers to zero and the min_subsequence to an empty string
    index_s1, index_s2 = 0, 0
    min_subsequence = ""

    # iterate over str1
    while index_s1 < size_str1:
        # check if the character pointed by index_s1 in str1
        # is the same as the character pointed by index_s2 in str2
        if str1[index_s1] == str2[index_s2]:
            # if this was the first character of str2, mark it as the start of the substring
            if index_s2 == 0:
                start = index_s1
            
            # if the pointed character is the same in both strings increment index_s2
            index_s2 += 1
            
            # check if a valid substring has been found
            if index_s2 == size_str2:
                end = index_s1

                # update min_sub_len and min_subsequence if current subsequence is shorter
                if end - start + 1 < min_sub_len:
                    min_sub_len = end - start + 1
                    min_subsequence = str1[start : end + 1]

                # set index_s1 to end + 1 to continue checking in str1
                # after this discovered subsequence
                index_s1 = end + 1
                index_s2 = 0
                continue

        # increment pointer index_s1 to check next character in str1
        index_s1 += 1

    # return the minimum window subsequence
    return min_subsequence

# driver code
def main():
    str1 = ["abcdebdde", "fgrqsqsnodwmxzkzxwqegkndaa", "zxcvnhss", "alpha", "beta"]
    str2 = ["bde", "kzed", "css", "la", "ab"]

    # let's uncomment the following test case and verify the result
    # str1.append("abcdedeaqdweq")
    # str2.append("aqeq")

    for i in range(len(str1)):
        print(i+1, ". \tInput string: (" + str1[i]+", " + str2[i]+")", sep="")
        print("\tSubsequence string: ", min_window(str1[i], str2[i]))
        print("-"*100)

if __name__ == '__main__':
    main()