Find longest substring without repeating characters

Question

Given a string S of length N find longest substring without repeating characters.

Example:

Input:

Answer 1

The solution in C.

#include
#include 

void longstr(char* a, int *start, int *last)
{
    *start = *last = 0;
    int visited[256];
    for (int i = 0; i < 256; i++)
    {
        visited[i] = -1;
    }
    int max_len = 0;
    int cur_len = 0;
    int prev_index;
    visited[a[0]] = 0;
    for (int i = 1; i < strlen(a); i++)
    {
        prev_index = visited[a[i]];
        if (prev_index == -1 || i - cur_len > prev_index)
        {
            cur_len++;
            *last = i;
        }
        else
        {
            if (max_len < cur_len)
            {
                *start = *last - cur_len;
                max_len = cur_len;
            }
            cur_len = i - prev_index;
        }
        visited[a[i]] = i;
    }
    if (max_len < cur_len)
    {
        *start = *last - cur_len;
        max_len = cur_len;
    }
}

int main()
{
    char str[] = "ABDEFGABEF";
    printf("The input string is %s \n", str);
    int start, last;
    longstr(str, &start, &last);
    //printf("\n %d  %d \n", start, last);
    memmove(str, (str + start), last - start);
    str[last] = '\0';
    printf("the longest non-repeating character substring is %s", str);
    return 0;
}