Question

Strings have many convenient behaviors, one of which is that you can test whether a pattern occurs in another string, using the syntax pattern in original which produces a boolean result. We want you to implement this test from basic principles. Provide an implemenation of a function with calling signature isSubstring (pattern, original) that returns True or False, depending on the given parameters. Furthermore, you must not rely on any of the built-in behaviors of the string class, other than the fact that you can determine their lengths and you can use indexing to retrieve a single character of a string at a given index. That is, you are allowed to use syntaxes such as len(original) or pattern ], but you must not use any other eatures of the string class such as find, index, or slicking notation pattern [j1k] Instead use control structures to look for the pattern yourself, presumably testing every possible placement of where it might occur within the original string, and then testing character-by-character to see if you find a match

Answer 1

def isSubstring(pattern, original):
    for i in range(len(original)-len(pattern)+1):
        matched = True
        for j in range(len(pattern)):
            if original[i+j] != pattern[j]:
                matched = False
        if matched:
            return True
    return False


print(isSubstring('hello', 'hello world'))
print(isSubstring('world', 'hello world'))
print(isSubstring('llo wor', 'hello world'))
print(isSubstring('worlds', 'hello world'))