028 Implement strStr().py

'''
Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

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'''

class Solution(object):
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        if not needle:
            return 0
        if not haystack:
            return -1
        i = 0
        needleLength = len(needle)
        while i < len(haystack):
            a = haystack[i:i + needleLength]
            if haystack[i:i + needleLength] == needle:
                return i
            else:
                index = 0
                try:
                    index = needle.rindex(haystack[i + needleLength])
                except Exception:
                    i += needleLength + 1
                i += needleLength-index
        return -1


if __name__ == "__main__":
    assert Solution().strStr("abcdefg", "ab") == 0
    assert Solution().strStr("abcdefg", "bc") == 1
    assert Solution().strStr("abcdefg", "cd") == 2
    assert Solution().strStr("abcdefg", "fg") == 5
    assert Solution().strStr("abcdefg", "bcf") == -1