#include<stdio.h>
#include<ctype.h>
void removeduplicates(char *input,char *output){
int seen[123]={0};
int j=0;
for(int i=0;input[i] !='\0';i++){
char c=input[i];
if(!(isalnum(c)||isspace(c))){
printf("invalid input\n");
output[0]='\0';
return;
}
if(!seen[(unsigned char)c] {
output[j++]=c;
seen[(unsigned char)c]=1;
}
}
output[j]='\0';
}
int main()
char input[]="programming in c";
char output[100];
removeduplicates(input, output);
printf("%s\n",output);
return 0;
}