KMP算法

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#include <stdio.h>#include <string.h>int next[32] = {-999};/* 返回模式串T在母串S中第pos个字符的位置 *//* 调试小技巧 print x = value 或 set var x = value 可以改变gdb运行时变量的值 */int index_BM(char *S, char *T, int pos){    int i;    int j;    i = pos;    j = 0;     while ( (i < strlen(S)) && (j < strlen(T)) )    {        if (S[i] == T[j])        {            i++;            j++;        }        else        {            i = i - j + 1;             j = 0;        }    }    /* 注意strlen(T)意味着j的取值范围为0 ~ (strlen(T) - 1) */    if (strlen(T) == j)    {        return i - strlen(T);    }    else    {        return -1;    }}void get_next(char *T, int *next){    int k = -1;    int j = 0;    next[j] = k;    while (j < strlen(T))    {        if ( (k == -1) || (T[j] == T[k]) ) //注意等号是==，而不是=        {            ++k; // 注意是先加后使用            ++j;            next[j] = k;        }        else        {            k = next[k];         }    }}int index_KMP(char *S, char *T, int pos){    int i;    int j;    i = pos;    j = 0;     while ( (i < strlen(S)) && (j < strlen(T)) )    {        /* j = -1 表示next[0], 说明失配处在模式串T的第0个字符。所以这里特殊处理，然后令i+1和j+1。*/        if ( (j == -1)  || S[i] == T[j])        {            i++;            j++;        }        else        {            j = next[j];        }    }    if (strlen(T) == j)    {        return i - strlen(T);    }    else    {        return -1;    }}void print_next(int next[], int n){   int i;   for (i = 0; i < n; i++)    {       printf("next[%d] = %d\n", i, next[i]);   }}int main(){    char  s[30] = "ababcabcacbab";    char t[30] = "abgabm";    int pos = 0;    int index;    printf("================ BM ==============\n");    index = index_BM(s, t, pos);    printf("index = %d\n", index);    printf("================ KMP ==============\n");    get_next(t, next);    print_next(next, strlen(t));    index = index_KMP(s, t, pos);    printf("index = %d\n", index);    return 0;}
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