串的模式匹配；BF+KMP（C语言源代码）

/*************************************************
*    串的模式匹配;BF+KMP（C语言源代码）
*    2021/8/23
**************************************8***********/
#include<stdio.h>
#include<stdlib.h>
#define MAXSIZE 100

typedef struct
{
	char ch[MAXSIZE+1];
	int length;
}SString;


//①串的赋值操作
void StringAssign(SString* s1, char s2[])
{
    int i = 0;
    while (s2[i] != '\0')  // '\0' 是字符串的结束符，任何字符串之后都会自动加上'\0'
        i++;               //计算s2的长度
    s1->length = i;
    for (i = 0; i < s1->length; i++)
        s1->ch[i+1] = s2[i]; //从第一个字符开始逐个字符赋值
}

/*②BF算法*/
int index_BF(SString *S, SString *T)
{
    int i = 1, j = 1;
    while (i <=S->length && j <=T->length)
    {
        if (S->ch[i] == T->ch[j])
        {
            i++;
            j++;
        }
        else
        {
            i = i - j + 2;
            j = 1;
        }
    }
    if (j > T->length)
        return (i - T->length);
    else
        return 0;
    
}


/*③在使用KMP算法前，先求next[]数组*/
void Get_Next(SString* T, int next[])
{
    int i = 1; int j = 0;
    next[1] = 0;
    while (i < T->length)
    {
        if (j == 0 || T->ch[i] == T->ch[j])
        {
            i++; j++; next[i] = j;
        }
        else
            j = next[j];   /*模式失配，模式串向前移动*/
    }
}



/*④求修正后的nextval[]数组*/
void Get_Nextval(SString* T, int nextval[])
{
    int i = 1; int j = 0;
    nextval[1] = 0;
    while (i < T->length)
    {
        if (j == 0 || T->ch[i] == T->ch[j])
        {
            i++; j++;
            if (T->ch[i] != T->ch[j])nextval[i] = j;
            else
                nextval[i] = nextval[j];
        }
        else
            j = nextval[j];   /*模式失配，模式串向前移动*/
    }
}


/*⑤KMP算法*/
int index_KMP(SString *S, SString *T,int next[])
{
    
    int i = 1, j = 1;
    while (i <= S->length && j <= T->length)
    {
        if (j==0||S->ch[i] == T->ch[j])
        {
            i++;
            j++;
        }
        else
        {
            j = next[j];   /*此处是KMP与BF的主要区别：1.i不用回溯 2.j不用回溯到j=1,而是回溯到效率更高的next[j]*/
        }
    }
    if (j > T->length)
        return (i- T->length);
    else
        return 0;

}


int main()
{
    /*定义串指针*/
    SString *s1= (SString*)malloc(sizeof(SString));
    SString *t2 = (SString*)malloc(sizeof(SString));
  
    /*定义字符串数组*/
    char S1[] = "abcdefjh";
    char T2[] = "defjh";

    /*①串的赋值操作*/
    StringAssign(s1,S1);
    //printf("%c",s1->ch[1]);
    StringAssign(t2, T2);
   // printf("\n%c", t2->ch[1]);


    /*②BF算法*/
    int a = 0;
    a=index_BF(s1,t2);
    printf("模式串在主串的第%d个位置\n\n", a);

    /*③在使用KMP算法前，先求next[]数组*/
    int next[6] = {0,0,0,0,0,0};
    Get_Next(t2, next);
    printf("next[j]数组元素为：");
    for (int i = 0; i < 5; i++)
    {
        printf("%d ", next[i+1]);
    }
    printf("\n\n");

    /*④求修正后的nextval[]数组*/
    int nextval[6] = { 0,0,0,0,0,0 };
    Get_Next(t2, nextval);
    printf("nextval[j]数组元素为：");
    for (int i = 0; i < 5; i++)
    {
        printf("%d ", nextval[i + 1]);
    }
    printf("\n\n");


    /*⑤在next[]数组下，使用KMP算法*/
    int b = 0;
    b = index_KMP(s1,t2, next);
    printf("模式串在主串的第%d个位置\n\n", b);

    /*⑤在nextval[]数组下，使用KMP算法*/
    int c = 0;
    c = index_KMP(s1, t2, nextval);
    printf("模式串在主串的第%d个位置\n", c);

    return 0;



}