Implement strStr().
Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Example 1:
Input: haystack = "hello", needle = "ll" Output: 2
Example 2:
Input: haystack = "aaaaa", needle = "bba" Output: -1
1 class Solution: 2 def strStr(self, haystack, needle): 3 """ 4 :type haystack: str 5 :type needle: str 6 :rtype: int 7 """ 8 if needle ==‘‘: 9 return 0 10 nexts=self.caclNext(needle) 11 ans = -1 12 i = 0 13 j = 0 14 while i < len(haystack): 15 if(j==-1 or haystack[i] == needle[j]): 16 i += 1 17 j += 1 18 else: 19 j = nexts[j] 20 if j == len(needle): 21 ans = i - len(needle) 22 break 23 return ans 24 25 def caclNext(self, p): 26 nexts = [0]*(len(p)) 27 nexts[0] = -1 28 k = -1 29 j = 0 30 while j < len(p) - 1: 31 if k == -1 or p[j] == p[k]: 32 k += 1 33 j += 1 34 nexts[j] = k 35 else: 36 k = nexts[k] 37 return nexts
