First non-repeating character in a stream

PROBLEM :
Given an input stream of n characters consisting only of small case alphabets the task is to find the first non repeating character each time a character is inserted to the stream.

Example

Flow in stream : a, a, b, c
a goes to stream : 1st non repeating element a (a)
a goes to stream : no non repeating element -1 (5, 15)
b goes to stream : 1st non repeating element is b (a, a, b)
c goes to stream : 1st non repeating element is b (a, a, b, c)

Input:
The first line of input contains an integer T denoting the no of test cases. Then T test cases follow. Each test case contains an integer N denoting the size of the stream. Then in the next line are x characters which are inserted to the stream.

Output:
For each test case in a new line print the first non repeating elements separated by spaces present in the stream at every instinct when a character is added to the stream, if no such element is present print -1.

Constraints:
1<=T<=200
1<=N<=500

Example:
Input:
2
4
a a b c
3
a a c

Output:
a -1 b b
a -1 c

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SIMPLE c++ IMPLEMENTATION :
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#include<bits/stdc++.h>
using namespace std;
#define CHAR 256

typedef struct NODE
{
    char data ;
    struct NODE *prev ;
    struct NODE *next ;
}node ;

void appendNode(node **head,node **tail,char ch)
{
    node *temp ;
    temp=new node() ;
   
    temp->data=ch ;
    temp->prev=NULL ;
    temp->next=NULL ;
   
    if((*head)==NULL)
    {
        (*head)=temp ;
        (*tail)=temp ;
        return ;
    }
   
    (*tail)->next=temp ;
    temp->prev=(*tail) ;
    (*tail)=temp ;
}

void removeNode(node **head,node **tail,node *temp)
{
    if(!(*head))
        return ;
       
    if((*head)==temp)
        (*head)=(*head)->next ;
       
    if((*tail)==temp)
        (*tail)=(*tail)->prev ;
       
    if(temp->next!=NULL)
        temp->next->prev=temp->prev ;
       
    if(temp->prev!=NULL)
        temp->prev->next=temp->next ;
       
    delete(temp) ;
}

int main()
{
int t ;
cin>>t ;
while(t--)
{
   int no ;
   cin>>no ;
 
   node *dll[CHAR] ;
   bool repeat[CHAR] ;
 
   for(int i=0;i<CHAR;i++)
   {
       dll[i]=NULL ;
       repeat[i]=false ;
   }
 
   node *head,*tail ;
   head=NULL ;
   tail=NULL ;
 
   while(no--)
   {
       char ch ;
       cin>>ch ;
     
       if(!repeat[ch])
       {
           if(dll[ch]==NULL)
           {
               appendNode(&head,&tail,ch) ;
               dll[ch]=tail ;
           }
           else
           {
               removeNode(&head,&tail,dll[ch]) ;
               dll[ch]=NULL ;
               repeat[ch]=true ;
           }
       }
     
       if(head)
           cout<<head->data<<" " ;
       else
           cout<<-1<<" " ;
   }
 
   cout<<endl ;
}
return 0;
}

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SIMPLE c++ IMPLEMENTATION : (another solution) : Queue
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#include<bits/stdc++.h>
using namespace std;
#define CHAR 256

int main()
{
int t ;
cin>>t ;
while(t--)
{
   int no ;
   cin>>no ;
 
   queue<char> que ;
   int charcount[CHAR]={0} ;
 
   while(no--)
   {
       char ch ;
       cin>>ch ;
     
       que.push(ch) ;
       charcount[ch]++ ;
     
       while(!que.empty())
       {
           if(charcount[que.front()]>1)
               que.pop() ;
           else
           {
               cout<<que.front()<<" " ;
               break ;
           }
       }
     
       if(que.empty())
           cout<<-1<<" " ;
   }
 
   cout<<endl ;
}
return 0;
}

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