Leetcode 28 Implement strStr()

Implement strStr().

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

在一个字符串中查找另外一个字符串是否存在。

暴力 O(n^2):以原字符串的index为指针，每次都检测接下来一段是否与子字符串一样。

class Solution:
    # @param {string} haystack
    # @param {string} needle
    # @return {integer}
    def strStr(self, haystack, needle):
        if needle == '':
            return 0
        for i in range(len(haystack)-len(needle)+1):
            if haystack[i:i+len(needle)] == needle:
                return i
        return -1

KMP算法 O(n): https://en.wikipedia.org/wiki/Knuth–Morris–Pratt_algorithm

http://blog.csdn.net/v_july_v/article/details/7041827

失配时，模式串向右移动的位数为：已匹配字符数 - 失配字符的上一位字符所对应的最大长度值

def str_str(string, substring)return 0 if substring == ''
   
   # create failure function table
   pos = 2
   cnd = 0
   failure_table = [-1, 0]
   while pos < substring.length
     if substring[pos - 1] == substring[cnd]
       failure_table[pos] = cnd + 1
       pos += 1
       cnd += 1
     elsif cnd > 0
       cnd = failure_table[cnd]
     else
       failure_table[pos] = 0
       pos += 1
     end
   end

   m = i = 0
   while m + i < string.length
     if substring[i] == string[m + i]
       i += 1
       return m if i == substring.length
     else
       m = m + i - failure_table[i]
       i = failure_table[i] if i > 0
     end
   end
   -1
end