KMP模板

Posted 2020-12-09 mrs-jiangmengxia

KMP

? KMP算法每当一趟匹配过程中出现字符比较不等时，主串S中的i指针不需回溯，而是利用已经得到的“部分匹配”结果将模式向右“滑动”尽可能远的一段距离后，继续进行比较。

? KMP算法的主要核心其实就是next数组的求解

next数组求解

void GetNext(char *w, int next[])
{
	//w为模式串
    memset(next, 0, sizeof(next));
    int i, j, len;
    i = 0;
    j = -1;
    next[0] = -1;
    len = strlen(w);
    while(i < len)
    {
        if(j == -1 || w[i] == w[j])
        {
            i++;
            j++;
            if(w[i] != w[j])
                next[i] = j;
            else
                next[i] = next[j];
        }
        else    j = next[j];
    }
}

字符串匹配

int kmp(char *s, char *p, int next[])
{
    int s_len = strlen(s);
    int p_len = strlen(p);
    int i = 0;
    int j = 0;
    int cnt  = 0;
    while(i < s_len && j < P_len)
    {
        if(j == -1 || s[i] == p[j])
        {
            i++;
            j++;
        }
        else    j = next[j];
    }
    if(j == p_len)	return i-j;
    else			return -1;
}

总代码

#include<stdio.h>
#include<string.h>
int next[1000005];
char w[1000005];
char t[1000005];
void GetNext(char *w, int next[])
{
    memset(next, 0, sizeof(next));
    int i, j, len;
    i = 0;
    j = -1;
    next[0] = -1;
    len = strlen(w);
    while(i < len)
    {
        if(j == -1 || w[i] == w[j])
        {
            i++;
            j++;
            if(w[i] != w[j])
                next[i] = j;
            else
                next[i] = next[j];
        }
        else    j = next[j];
    }
}
int kmp(char *s, char *p, int next[])
{
    int s_len = strlen(s);
    int p_len = strlen(p);
    int i = 0;
    int j = 0;
    while(i < s_len && j < p_len)
    {
        if(j == -1 || s[i] == p[j])
        {
            i++;
            j++;
        }
        else    j = next[j];
    }
    if(j == p_len)  return i - j;
    else            return -1;
}
int main()
{
    scanf("%s", w);
    scanf("%s", t);
    GetNext(w, next);
    if(kmp(t, w, next) != -1)     printf("匹配成功
");
    else                          printf("匹配失败
");
    return 0;
}