kmp算法

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

int kmp(const char *str, const char *str_sub){
    int sub_len = strlen(str_sub);
    if(sub_len == 0){ 
        return 0;
    }   
    int* next = (int*) calloc(sizeof(int), sub_len);
    int i = 0;
    int j = -1; 
    next[0] = -1; 
    while(i < sub_len){
        if(j == -1 || str_sub[i] == str_sub[j]){
            ++i;
            ++j;
            next[i] = j;
        } else {
            j = next[j];
        }   
    }   

    int len = strlen(str);

    for(i = -1, j = -1; i < len && j < sub_len; ){
        if(j == -1 || str[i] == str_sub[j]){
            ++i;
            ++j;
        } else {
            j = next[j];
        }   
    }   

    free(next);
    if(j >= sub_len){
        return i - sub_len;
    }  else {
        return -1; 
    }   
}

int main(){
    char *str = "hello";
    char *str_sub = "llo";
    printf("str:%s, sub:%s, %d
",str, str_sub, kmp(str, str_sub));
    str = "ababababb";
    str_sub = "abababb";
    printf("str:%s, sub:%s, %d
",str, str_sub, kmp(str, str_sub));
    str = "hello";
    str_sub = ""; 
    printf("str:%s, sub:%s, %d
",str, str_sub, kmp(str, str_sub));
    str = "hello";
    str_sub = "hellol";
    printf("str:%s, sub:%s, %d
",str, str_sub, kmp(str, str_sub));
    return 0;
}