September 11th 2024 Questions

2010_message_transmission_error_1.py

t = "#" + input()
n = len(t)
longest_valid = ""

for i in range(2, n):
    left_substring = t[1 : i + 1]
    right_substring = t[i : i + len(left_substring)]
    # print(f"left sub: {left_substring}; right sub: {right_substring}")
    if left_substring == right_substring:
        if len(left_substring) > len(longest_valid):
            longest_valid = left_substring
else:
    if len(longest_valid) != 0:
        print("YES")
        print(longest_valid)
    else:
        print("NO")

2010_message_transmission_error_2.py

t = input()
n = len(t)
longest_valid = ""

for i in range(1, n):
    substring = t[: i + 1]
    if len(substring) <= n // 2:
        continue

    if t.startswith(substring) and t.endswith(substring):
        # print(t[i + 1 : i + len(substring) + 1])
        if (
            substring != t[i + 1 : i + len(substring) + 1]
            and len(substring) > len(longest_valid)
            and len(substring) < len(t)
        ):
            longest_valid = substring
else:
    if len(longest_valid) != 0:
        print("YES")
        print(longest_valid)
    else:
        print("NO")

2010_message_transmission_error_optimized.py

t = input()
n = len(t)
longest_valid = ""

for i in range(1, n):
    # get the substring from the start to index i (including)
    substring = t[: i + 1]

    # eliminating conditions
    if (
        # if the length of the substring is less than half of the message string, then it can't be the OG string
        len(substring) <= n // 2
        # the length of substring should not exceed the message string the it can't be the OG string
        or len(substring) >= len(t)
        # for case abcabc - appending one message after the another is not an error
        or substring == t[i + 1 : i + len(substring) + 1]
    ):
        continue

    # acceptance conditions
    if (
        # the message string should start and end with the substring
        t.startswith(substring)
        and t.endswith(substring)
        # update the longest_valid if the current length of the substring is greater
        and len(substring) > len(longest_valid)
    ):
        longest_valid = substring
else:
    if len(longest_valid) != 0:
        print("YES")
        print(longest_valid)
    else:
        print("NO")