字符串匹配算法BF、KMP、BM的python实现。

# BF算法
def BF(str1,str2):
    halen = len(str1)
    nelen = len(str2)
    j = 0
    for i in range(halen):
        if j == nelen:
            break
        if str1[i] == str2[j]:
            j = j+1
        else:
            i -= j
            j = 0
    if j == nelen:
        renum = i - nelen
    else:
        renum = -1
    return renum

#KMP算法
def getNextList(s):
    n =len(s)
    nextList = [0,0]
    j = 0
    for i in range(1,n):
        while j >0 and s[i] != s[j]:
            j = nextList[j]
        if s[i] == s[j]:
            j += 1
        nextList.append(j)
    return nextList

def KMP(str1,str2):
    n = len(str1)
    m = len(str2)
    nextList = getNextList(str2)
    indies = []
    j = 0
    for i in range(n):
        while str1[i] != str2[j] and j>0:
            j =nextList[j]
        if str1[i] == str2[j]:
            j += 1
            if j == m:
                indies.append(i-m+1)
                j = nextList[j]
    return indies

#BM算法
def getBMBC(s):
    BMBC = dict()
    for i in range(len(s)-1):
        char = s[i]
        BMBC[char] = i+1
    return BMBC

def getBMGS(s):
    BMGS = dict()
    BMGS[''] = 0
    for i in range(len(s)):
        GS = s[len(s)-i-1]
        for j in range(len(s)-i-1):
            NGS = s[j:j+i+1]
            if GS == NGS:
                BMGS[GS] = len(s)-i-j-1
    return BMGS

def BM(str1,str2):
    n = len(str1)
    m = len(str2)
    i = 0
    j = m
    indies = []
    BMBC = getBMBC(str2)
    BMGS = getBMGS(str2)
    while i < n:
        while j > 0:
            if i + j - 1 >=n:
                return indies
            a = str1[i+j-1:i+m]
            b = str2[j-1:]
            if a == b:
                j = j-1
            else:
                i = i + max(BMGS.setdefault(b[1:],m),j-BMBC.setdefault(str1[i+j-1],0))
                j = m
            if j == 0:
                indies.append(i)
                i+=1
                j = len(str2)

参考资料：字符串匹配的KMP算法 - 阮一峰的网络日志 (ruanyifeng.com)、字符串匹配的Boyer-Moore算法 - 阮一峰的网络日志 (ruanyifeng.com)、algorithm-base/BF算法.md at main · chefyuan/algorithm-base · GitHub、字符串匹配BF算法、KMP算法以及BM算法Python实现_BetterManPeter的博客-CSDN博客