字符串匹配Sunday算法实现

  今天稍稍度娘了一下匹配字符串的算法，主要搜索结果还是源自CSDN。其中一篇《字符串匹配算法总结》介绍了好几种字符串匹配算法，写的非常好。我挑了其中作者也比较推崇，比较新，效能比较好，算法又比较简单的Sunday算法，稍加揣摩，然后发现贴的实现代码，居然和算法描述的从右往左比对是冲突的，因此我断定贴的代码是错的。仔细看就能发现从左向右比对，很容易会跳过一种匹配，如从a1a1a2寻找a1a2,就会匹配失败(?也许也是对的)。

  下面是我做的实现，融入到我的‘类string’类的find实现当中了。对于其他网贴的实现方式略有调整。对于JAssert，data_->len() 这种未解释的小东西，相信读者您都明白是啥。

[code]//#define SupportLongSubString
#ifdef SupportLongSubString  //用于支持较长的sub字符串
    typedef unsigned short OCCType;
#else
    typedef unsigned char OCCType;
#endif
size_t JinString::find(const char *sub, size_t startPos)
{
    if(!data_ || data_->len()<startPos)return STRNPOS;
    ///[Sun 90] D.M. Sunday: A Very Fast Substring Search Algorithm. Communications of the ACM, 33, 8, 132-142 (1990)
    /// http://www-igm.univ-mlv.fr/~lecroq/string/     /// http://www.iti.fh-flensburg.de/lang/algorithmen/pattern/sundayen.htm     /// http://blog.csdn.net/force_eagle/article/details/10340907     ///[Sunday算法]根据网上的算法，纠错、调整、改进
    //预处理和strlen一起做,原本算法这个数组是要预计算移位数，但是我不先计算长度
    //所以重新约定occ[]值v含义：len-(v-1）= len-v+1 = 需移动的字节数. v=0表示无法匹配需要移动len+1字节
    OCCType occ[256];
    memset(occ,0,256);
    int subLen=0;
    unsigned char ch;
    while((ch = (unsigned char)sub[subLen])){
        occ[ch] = (OCCType)++subLen;
    }
    JAssert(subLen<(1<<(sizeof(OCCType)*8)));  //断言subString长度不可越界
    if(subLen+startPos>data_->len())return STRNPOS;

    for(int matchAt=1;matchAt<=subLen;matchAt++)
    {
        if(data_->buf()[startPos + subLen - matchAt]
                != sub[subLen - matchAt])
        {  //如果不匹配，按算法移动startPos重新匹配
           startPos += subLen - occ[(unsigned char) (data_->buf()[startPos + subLen])] + 1;
           if(subLen+startPos>data_->len())return STRNPOS;
           matchAt = 0;
        }
    }
    return startPos;
}

  代码通过了以下的测试：

[code]void TestJinString::unitTest()
{
    JinString strs,strm,strjzy;
    strs = "abcdefghijklmn";
    strm = "MMMMM";
    strjzy = "jzyajzybjzyajzyz";
    JinString subjzy("jzyajzyz");

    //JinString str("abcdefghijklmnMMMMMjzyajzybjzyajzyzMMMMMabcdefghijklmn")
    JinString str;
    str += strs;
    str = str + strm + strjzy + strm + strs;

    JAssert(str.find(subjzy) ==  strs.length() + strm.length() + 8);
    JAssert(str.find(strs) == 0);
    JAssert(str.find(strm) == strs.length());
    JAssert(str.find(strs,str.find(strm)) == strs.length() + strm.length()*2 + strjzy.length());
    JAssert(str.find("jzyajzybjzyc")==STRNPOS);
}

文章首发地址 http://blog.csdn.net/d0cking/article/details/40689685 也是俺写滴……