KMP算法

 

这个算法看了。很久啊。很难懂。。虽说现在会了。。不过。应用的根本不熟练

老规矩。。。贴下代码。。纪念下。

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

typedef struct
{
    char *ch;
    int length;
}SString;

int strKMP(SString *S,SString *T,int pos,int next[]);    //求在主窜中S中第pos个字符之后的位置的KMP算法
void get_next(SString *T,int next[]);    //求模式串中T的next函数值并存入数组next
int StrAssign(SString *str,char *chars);    ///生成一个与chars相等的字符串


int main()
{
    SString S={NULL,0},T={NULL,0};
    int pos;
    int next[50];
    StrAssign(&S,"ababcabcacbab");
    StrAssign(&T,"cacba");
    get_next(&T,next);

    pos=strKMP(&S,&T,0,next);
    printf("%d\n",pos);
    return 0;
}
int StrAssign(SString *str,char *chars)
{
    if(str->ch)        //清空str
        free(str->ch);
    str->ch = (char *)malloc((strlen(chars)+1)*sizeof(char));
    if( !str->ch )
        return 0;
    str->length = strlen(chars);
    strcpy(str->ch,chars);    //复制字符串

    return str->length;
}

int strKMP(SString *S,SString *T,int pos,int next[])
{
    int i=pos,j=0;
    while(i < S->length && j < T->length)
    {
        if(j==-1 || S->ch[i] == T->ch[j])
        {
            i++;
            j++;
        }
         else
            j = next[j];
    }
    if(j >= T->length)
        return i - (T->length);
    else
        return -1;
}

void get_next(SString *T,int next[])
{
    int i=0,j=-1;
    next[0]=-1;
    while(i < T->length-1)    //这里注意下
    {
        if(j==-1 || T->ch[i] == T->ch[j])
        {
            i++; j++;
            if(T->ch[i] != T->ch[j])
                next[i]=j;
            else
                next[i] = next[j];
        }
        else
            j = next[j];
    }
    
}