python写算法题：leetcode: 28. Implement strStr()

https://leetcode.com/problems/implement-strstr/#/description

class Solution(object):
    def kmpTab(self, needle):
        nlen = len(needle)
        tab  = [0]*nlen
        j    = 0
        for i in xrange(1, nlen):
            while j>0 and needle[j] != needle[i]:
                j = tab[j-1]
            if needle[j] == needle[i]:
                j = j+1
            tab[i] = j
        return tab


    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        tab = self.kmpTab(needle)
        hslen = len(haystack)
        ndlen = len(needle)
        if hslen==0 and ndlen==0: return 0
        i=0
        j=0
        while i<hslen and j<ndlen:
            if haystack[i] != needle[j]:
                if j>0:
                    j=tab[j-1]
                else:
                    j=0
                    i+=1
            else:
                i+=1
                j+=1
        if j>=ndlen:
            return i-ndlen
        return -1

思路：KMP