KMP快速查找字符串

淡淡的烟草味﹌ 2022-06-17 14:10 186阅读 0赞

问题描述：  
使用KMP算法快速查找字符串（可支持中文）

PS：  
解析KMP的方法虽然多种多样，但是我仍然最喜欢数据结构书中我认为最经典的那种  
![这里写图片描述][SouthEast]

![这里写图片描述][SouthEast 1]

参考代码：

#include <iostream>
    #include <string>
    #include <vector>
    using namespace std;
    
    int KMPAlgorithm(const wstring& strText, const wstring& strPattern, int *m_pNext, int nStartPos)
    {
        int i = nStartPos;
        int j = 0;
    
        while (i < (int)strText.size() && j < (int)strPattern.size())
        {
            if (j == -1 || strText[i] == strPattern[j])
            {
                ++i;
                ++j;
            }
            else
            {
                j = m_pNext[j];
            }
        }
        if (j == strPattern.size())
            return (i - j);
    
        return -1;
    }
    
    void GetNextVal(const wstring& strPattern, int *m_pNext)
    {
        int j = 0;
        int k = -1;
        m_pNext[0] = -1;
    
        while (j < (int)strPattern.size())
        {
            if (k == -1 || strPattern[j] == strPattern[k])
            {
                ++j;
                ++k;
                if (strPattern[j] != strPattern[k])
                    m_pNext[j] = k;
                else
                    m_pNext[j] = m_pNext[k];
            }
            else
            {
                k = m_pNext[k];
            }
        }
    }
    
    void GetAllSubPos(const wstring& strText, const wstring& strPattern, std::vector<int>& vecans)
    {
        size_t szlen = strPattern.size();
        int *m_pNext = new int[strPattern.size() + 1];
        memset(m_pNext, 0, (strPattern.size() + 1) * sizeof(int));
    
        if (strText.size() == 0 || strPattern.size() == 0)
            return;
    
        GetNextVal(strPattern, m_pNext);
    
        vecans.clear();
        int nPos = 0;
        while (1)
        {
            nPos = KMPAlgorithm(strText, strPattern, m_pNext, nPos);
            if (nPos == -1)
                break;
    
            vecans.push_back(nPos);
            nPos++;
        }
    
        delete[]m_pNext;
    }
    
    int main(int argc, char*argv[])
    {
        vector<int>ansvec;
        wstring strText;
        wstring strPattern;
        printf("输入主串: ");
        getline(wcin, strText);
        printf("输入模式串: ");
        getline(wcin, strPattern);
        GetAllSubPos(strText, strPattern, ansvec);
        if (ansvec.size() > 0)
            printf("输入所有查找结果:\n");
        else
            printf("没有查到\n");
        for (int i = 0; i < (int)ansvec.size(); i++)
        {
            wstring strSub = strText.substr(ansvec[i]);
            wcout << strSub << endl;
        }
    
        return 0;
    }

运行结果：  
![这里写图片描述][SouthEast 2]

[SouthEast]: /images/20220617/dde3eb33e19e480290d1ff1684f45ee2.png
[SouthEast 1]: /images/20220617/6f964bec70b24f03ad899edc4901a8cb.png
[SouthEast 2]: /images/20220617/8dd754083df14b5983b9883ec1e96862.png