Question

here is a general implementation

int stridx (char[] src, char[] str){
    int i,j,k;
    for(i=0;i < (src.len - str.len);i++){
      for(j=i,k=0; str[k] != '\0' && str[k] == src[i]; j++,k++);
      if( k> 0 && str[k]=='\0') return i;
    }
    return -1;
}

The worst case of the algorithm could be n^2, if we have aaaaaaaaaaaaaaaaaaaaaaaa (assuming both src and str are very long, and the length of them is very close).

Can I have a better algorithm?

Answer 1

You could use the Boyer-Moore algorithm, which is O(n). Here’s sample C code.