KMP算法笔记

来源：互联网发布：丰田车导航软件编辑：程序博客网时间：2024/06/05 05:07

从开始了解学习KMP到现在已经第三遍了…………借着项目写RKR-GST算法也用到字符串模式匹配，顺便再把KMP弄清楚些。

模式串为“abaabcaba”:

next[j] = k 代表p[j] 之前的模式串子串中，有长度为k 的相同前缀和后缀。

next[j+1] 对于pattern的前j+1个序列字符：

若pattern[k] == pattern[j]，则next[j + 1 ] = next [j] + 1 = k + 1；
若pattern[k ] ≠ pattern[j]，如果此时pattern[ next[k] ] == pattern[j ]，则next[ j + 1 ] = next[k] + 1，否则继续递归重复此过程。

#include <iostream>#include <cstring>using namespace std;int violentMatch(char *s, char *p){    int sLen = (int)strlen(s);    int pLen = (int)strlen(p);        int i = 0, j = 0;    while (i < sLen && j < pLen)    {        if (s[i] == p[j])        {            //①如果当前字符匹配成功（即S[i] == P[j]），则i++，j++            i++;            j++;        }        else        {            //②如果失配（即S[i]! = P[j]），令i = i - (j - 1)，j = 0            i = i - j + 1;            j = 0;        }    }    //匹配成功，返回模式串p在文本串s中的位置，否则返回-1    if (j == pLen)        return i - j;    else        return -1;}void initNext(char *p, int next[]){    int pLen = (int)strlen(p);    next[0] = -1;    int k = -1;    int j = 0;    while (j < pLen - 1)    {        //p[k]表示前缀，p[j]表示后缀        if (k == -1 || p[j] == p[k])        {            ++j;            ++k;            next[j] = k;        }        else        {            k = next[k];        }    }}void myInitNext(char *p, int next[]){    int pLen = (int)strlen(p);    next[0] = -1;    for (int j = 0, k = -1; j < pLen - 1; j++)    {        while (!(k == -1 || p[j] == p[k]))<span style="white-space:pre"></span>//“递归”向前查找            k = next[k];        next[j+1] = ++k;    }}int kmpSearch(char *s, char *p, int next[]){    int i = 0, j = 0;    int sLen = (int)strlen(s);    int pLen = (int)strlen(p);    while (i < sLen && j < pLen)    {        //①如果j = -1，或者当前字符匹配成功（即S[i] == P[j]），都令i++，j++        if (j == -1 || s[i] == p[j])        {            i++;            j++;        }        else        {            //②如果j != -1，且当前字符匹配失败（即S[i] != P[j]），则令 i 不变，j = next[j]            //next[j]即为j所对应的next值            j = next[j];        }    }    if (j == pLen)        return i - j;    else        return -1;}int myKMPSearch(char *s, char *p, int next[]){    int sLen = (int)strlen(s);    int pLen = (int)strlen(p);        for (int i = 0, j = 0; i < sLen; i++, j++)    {        if (j == pLen)            return i - j;        else if (j == -1)            j = 0;        if (s[i] != p[j])            j = next[j];    }    return -1;}int myKMPSearch1(char *s, char *p, int next[]){    int sLen = (int)strlen(s);    int pLen = (int)strlen(p);        for (int i = 0, j = 0; i < sLen; i++, j++)    {        if (j == pLen)            return i - j;        if (s[i] != p[j])            j = max(next[j], 0);    }    return -1;}int myKMPSearch2(char *s, char *p, int next[]){    next[0] = 0;    int sLen = (int)strlen(s);    int pLen = (int)strlen(p);        for (int i = 0, j = 0; i < sLen; i++, j++)    {        if (j == pLen)            return i - j;        if (s[i] != p[j])            j = next[j];    }    return -1;}int main(int argc, const char * argv[]){    char s[] = "BBC ABCDAB ABCDABCDABDABABE";    char p[] = "ABCDABC";        int matchPos;        int next[100];    initNext(p, next);    for (int i = 0; i < strlen(p); i++)        cout << next[i] << " ";    cout << endl;        matchPos = kmpSearch(s, p, next);    cout << matchPos << endl;        myInitNext(p, next);    for (int i = 0; i < strlen(p); i++)        cout << next[i] << " ";    cout << endl;        matchPos = myKMPSearch(s, p, next);    cout << matchPos << endl;        cout << "myKMPSearch1:" << endl;    matchPos = myKMPSearch1(s, p, next);    cout << matchPos << endl;        cout << "myKMPSearch2:" << endl;    matchPos = myKMPSearch2(s, p, next);    cout << matchPos << endl;        cout << "violentMatch:" << endl;        matchPos = violentMatch(s, p);    cout << matchPos << endl;            return 0;}

详细KMP算法参考：http://blog.csdn.net/v_july_v/article/details/7041827

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