Remove Duplicate Characters from a String

Code

#include <stdio.h>
#include <stdint.h>

void remove_duplicates(char *str) {
	char dup[0xff]={0};
    int slow=0,fast=0;
    while(str[fast]){
        if(!dup[str[fast]]){
            dup[str[fast]]=1;
            str[slow++]=str[fast];
        }
        fast++;
    }
    while(slow<fast) str[slow++]=NULL;
}
int main() {
    char str[101];
    fgets(str, sizeof(str), stdin);

    // Remove newline
    uint8_t i = 0;
    while (str[i]) {
        if (str[i] == '\n') {
            str[i] = '\0';
            break;
        }
        i++;
    }

    remove_duplicates(str);
    printf("%s", str);
    return 0;
}

Solving Approach