Remove Duplicate Characters from a String

Code

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

void remove_duplicates(char *str) {
	int seen[256] = { 0 };
    int i = 0;
    while (str[i] != '\0') {
        if (seen[str[i]]) {
            // shift rest of string downwards
            int insert = i;
            int lead = i + 1;
            while (str[lead] != '\0') {
                if (!seen[str[lead]]) {
                    str[insert++] = str[lead++];
                } else {
                    lead++;
                }
            }
            str[insert] = '\0';
        }
        seen[str[i]]++;
        i++;
    }
}

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