KMP算法

//复杂版
#include<stdio.h>
#include<stdlib.h>
#include<string.h>

void prefix_table(char pattern[],int prefix[],int n){
    prefix[0] = 0;
    int len   = 0;
    int i = 1;
    while (i < n){
        if (pattern[i] == pattern[len]){
            len++;
            prefix[i] = len;
            i++;
        }
        else{
            if (len > 0){
                len = prefix[len - 1];
            }
            else{
                prefix[i] = len;
                i++;
            }
        }
    }
}

int move_prefix_table(int prefix[],int n){
    int i;
    for(i=n-1;i>0;i--){
        prefix[i] = prefix[i-1];
    }
    prefix[0] = -1;
}

void kmp_search(char text[],char pattern[]){
    int  n = strlen(pattern);
    int  m = strlen(text);
    int *prefix = (int*)malloc(sizeof(int)*n);
    prefix_table(pattern,prefix,n);
    move_prefix_table(prefix,n);

    // text[i]     , len(text)    = m
    // pattern[j], len(pattern) = n
    int i = 0;
    int j = 0;
    while (i < m){
        if (j == n - 1 &&text[i] == pattern[j]){
            printf("Found patern at %d
", i - j );
            j = prefix[j];
            for (int x=0;x<n;x++){
                printf("%c",pattern[x]);
            }
        }
        if (text[i] == pattern[j]){
            i++; j++;
        }
        else{
            j = prefix[j];
            if (j == -1){
                i++; j++;
            }
        }
    }
}

int main(){
    
    char pattern[] = "ABABCABAA";
    char text[]    = "ABABABCABAABABABAB";
    
    kmp_search(text,pattern);
    /*
    int prefix[9];
    int n = 9;
    
    prefix_table(pattern,prefix,n);
    move_prefix_table(prefix,n);
    int i;
    for (i = 0;i < n;i++){
        printf("%d
",prefix[i]);
    }
    */
    return 0;
}

//精简版
#include<stdio.h>
#include<string.h>
#define maxn (int)1e5+8

char pattern[maxn]= {0},text[maxn]= {0};
int next[maxn]= {0};
void Next(char *s,int *fail) {
    fail[0]=-1,fail[1]=0;
    int len=strlen(s);
    for(int i=1,j=0;i<len;) {
        if(j==-1||s[i]==s[j])fail[++i]=++j;
        else j=fail[j];
    }
}

int KmpSearch(char* s, char* p) {
    int i = 0,j = 0,sLen = strlen(s),pLen = strlen(p);
    while (i < sLen && j < pLen) {
        if (j == -1 || s[i] == p[j]) 
            i++,j++;
        else j = next[j];
    }
    return j == pLen?i - j:-1;
}

int main() {
    scanf("%s%s",pattern,text);
    Next(pattern,next);
    printf("%d
",KmpSearch(text,pattern));
}