KMP算法C代码

 

贴上C代码作参考，关于算法，可以参考网上的博文，但不要参考太多，一两篇相近的即可。

 

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* 获取pattern的next数组 */
void get_next(char * pattern, int * next, int len)
{
    int i, index;
    for (next[0]=-1, i=1; i<len; i++)
    {
        if (pattern[i] == pattern[next[i-1]+1])
        {
            next[i] = next[i-1] + 1;
            continue;
        }
        for (index=next[i-1], next[i]=-1; index!=-1; index = next[index])
        {
            if (pattern[index+1] == pattern[i])
            {
                next[i] = index + 1;
                break;
            }
        }
    }
}

int KMP(char * text, int tlen, char * pattern, int plen, int * ptr)
{
    int i=0, tindex=0, pindex=0, count=0,  * next = malloc(sizeof(int) * plen);
    get_next(pattern, next, plen);
    while (i < tlen)
    {
        if (pattern[pindex] == text[i])
        {
            i ++;
            pindex ++;
            if (pindex == plen)
            {
                pindex = 0;
                ptr[tindex++] = i-plen;
            }
            continue;
        }
        if (pindex == 0)
        {
                i ++;
        }
        else
        {
            pindex = next[pindex-1] + 1;
        }
    }
    free(next);
    return tindex;
}

/* 按字符读入文件 */
int readText(const char * path, char * buf)
{
    FILE * f;
    int size;
    f = fopen(path, "r");
    if (!f)
    {
        return -1;
    }
    fseek(f, 0, SEEK_END);
    size = ftell(f);
    rewind(f);
    size = fread(buf, 1, size, f);
    if (size <= 0)
    {
        size = -1;
    }
    fclose(f);
    return size;
}

int main()
{
    char text[2000] = {0}, pattern[30] = "aba";//"abcabdecabcabcd";
    int * ptr, count = 0, plen, size = readText("file/text.txt", text), i=0, j;
    
    if (size <= 0)
    {
        return -1;
    }
    plen = strlen(pattern);
    ptr = malloc((size/plen)*sizeof(int));
    count = KMP(text, size, pattern, plen, ptr);
    printf("%d results.\n", count);
    while (i++ < count)
    {
        printf("index[%d] : ", i);
        for (j=0; j<plen; j++)
            printf("%c",text[ptr[i-1]+j]);
        printf("\n======================\n");
    }
    free(ptr);
    return 0;
}