[Leetcode][python]Implement strStr()/KMP算法

class Solution(object):
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        length = len(needle)
        for i in range(len(haystack) - len(needle) + 1):
            if haystack[i:i+len(needle)] == needle:
                return i
        return -1

class Solution:
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        if not haystack:
            if needle:
                return -1
            else:
                return 0
        if not needle:
            return 0
        return self.kmp_match(haystack, needle)

    #KMP
    def kmp_match(self, s, p):  
        m = len(s)
        n = len(p)  
        cur = 0  # 起始指针cur  
        table = self.partial_table(p)  
        # print(table)
        while cur <= m-n: # 长度不够就终止  
            # print("新一轮匹配，开始位置", cur)
            for i in range(n):  # 一次匹配长度  
                if s[i+cur] != p[i]:  
                    # print(s[i+cur], p[i], '不匹配。查表位置：', i, i - table[i-1])
                    cur += max(i - table[i-1], 1) # 有了部分匹配表,我们不只是单纯的1位1位往右移,可以一次移动多位  
                    break  
            else:
                return cur 
        return -1  

    #部分匹配表  
    def partial_table(self, p):  
        '''''partial_table("ABCDABD") -> [0, 0, 0, 0, 1, 2, 0]'''  
        prefix = set()  
        table = [0]  
        for i in range(1, len(p)):  # 从1开始进行前后缀比较  
            prefix.add(p[:i])  # 前缀每次累加就行
            postfix = set()
            for j in range(1, i+1):  # i+1 因为i需要包括
                postfix.add(p[j:i+1]) 
            # print(prefix, postfix)
            # print(prefix&postfix, len(prefix&postfix))
            # table.append(len((sorted((prefix&postfix),key = len)or {''}).pop()))
            if prefix&postfix:
                table.append(max(map(len,prefix&postfix)))
            else:
                table.append(0)
        return table