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  • KMP算法的C++实现

    这个问题阮一峰老师讲的很清楚,链接

    这里我只贴一下我的C++实现代码:

    #include <iostream>
    #include <cstring>
    #include <string>
    #include <set>
    #include <map>
    using namespace std;
    
    void BuildPatchMatchTable(int *partMatchTable, char *findstr)
    {
        if(findstr == NULL)
            return;
        partMatchTable[0] = 0;
        int sizefind = strlen(findstr);
        for(int i = 1; i < sizefind; ++i)
        {
            set<string> preset;
            string tmppre = "";
            tmppre = findstr[0];
            preset.insert(tmppre);
            for(int j = 1; j < i; ++j)
            {
                tmppre = tmppre + findstr[j];
                preset.insert(tmppre);
            }
    
            set<string> postset;
            string tmppost = "";
            tmppost = findstr[i];
            postset.insert(tmppost);
            for(int j = i - 1; j > 0; --j)
            {
                tmppost =  findstr[j] + tmppost;
                postset.insert(tmppost);
            }
            set<string> comset;
            for(set<string>::iterator beg = preset.begin(); beg != preset.end(); ++beg)
            {
                if(postset.count(*beg) > 0)
                    comset.insert(*beg);
            }
            int maxlen = 0;
            for(set<string>::iterator beg = comset.begin(); beg != comset.end(); ++beg)
            {
                if((*beg).size() > maxlen)
                    maxlen = (*beg).size();
            }
            partMatchTable[i] = maxlen;
        }
    }    
    
    int kmp(char *srcstr, char *findstr)
    {
        if(srcstr == NULL || findstr == NULL)
            return -1;
        int lensrc = strlen(srcstr);
        int lenfind = strlen(findstr);
        int *partMatchTable = new int[lenfind];
        BuildPatchMatchTable(partMatchTable, findstr);
        for(int i = 0; i < lenfind; ++i)
            cout << findstr[i] << "	" << partMatchTable[i] << endl;
        int curFind = 0;
        for(int i = 0; i < lensrc; )
        {
            if(findstr[curFind] == srcstr[i])
            {
                ++i;
                ++curFind;
            }
            else
            {
                if(curFind == 0)
                    ++i;
                else
                {
                    int movestep = curFind - partMatchTable[curFind-1];
                    i += movestep;
                    curFind = 0;
                }
            }
            if(curFind == lenfind)
            {
                delete []partMatchTable;
                return i - lenfind;
            }
        }
        return -1;
        delete []partMatchTable;
    }
    int main()
    {
        char srcStr[] = "bbc abcdab abcdabcdabde";
        char findStr[] = "abcdabd";
        cout << "pos:" << kmp(srcStr, findStr) << endl;
    
        char srcStr2[] = "bbc abcdab abcdabcdabdezzz";
        char findStr2[] = "zzz";
        cout << "pos:" << kmp(srcStr2, findStr2) << endl;
    
        char srcStr3[] = "bbc abcdab abcdabcdabde";
        char findStr3[] = "zzz";
        cout << "pos:" << kmp(srcStr3, findStr3) << endl;
    }

    关键问题

    1. 求出部分匹配值表

    2. 移动次数= 已匹配个数 - 最后一个匹配的字符的部分匹配结果

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  • 原文地址:https://www.cnblogs.com/kaituorensheng/p/3633700.html
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