[10/09, 2:52 pm] Vinith: #include <stdio.h>
#include <string.h>
#include <ctype.h>

int main() {
    char str[1000], result[1000];
    int seen[256] = {0};
    int k = 0;

    // Read full input line
    fgets(str, sizeof(str), stdin);

    // Check for invalid characters
    for (int i = 0; str[i]; i++) {
        if (!(isalnum(str[i]) || isspace(str[i]) || str[i]=='\n')) {
            printf("Invalid input");
            return 0;
        }
    }

    // Remove duplicates (ignore spaces in output)
    for (int i = 0; str[i]; i++) {
        char ch = str[i];
        if (ch == '\n' || ch == ' ') continue;  // ignore newline and spaces
        if (!seen[(unsigned char)ch]) {
            result[k++] = ch;
            seen[(unsigned char)ch] = 1;
        }
    }
    result[k] = '\0';

    printf("%s", result);
    return 0;
}