Problem:
Queue

Queue is a container of elements that are inserted and deleted according to FIFO (First In First Out).

For $n$ queues $Q_i$ ($i = 0, 1, ..., n-1$), perform a sequence of the following operations.

enqueue($t$, $x$): Insert an integer $x$ to $Q_t$.

front($t$): Report the value which should be deleted next from $Q_t$. If $Q_t$ is empty, do nothing.

dequeue($t$): Delete an element from $Q_t$. If $Q_t$ is empty, do nothing.

In the initial state, all queues are empty.

Input

The input is given in the following format.

$n \; q$
$query_1$
$query_2$
:
$query_q$

Each query $query_i$ is given by

0 $t$ $x$

or

1 $t$

or

2 $t$

where the first digits 0, 1 and 2 represent enqueue, front and dequeue operations respectively.

Output

For each front operation, print an integer in a line.

Constraints

$1 \leq n \leq 1,000$

$1 \leq q \leq 200,000$

$-1,000,000,000 \leq x \leq 1,000,000,000$

Sample Input 1

3 9
0 0 1
0 0 2
0 0 3
0 2 4
0 2 5
1 0
1 2
2 0
1 0

Sample Output 1

1
4
2

Solution in C (judge verdict: Accepted)

#include <stdio.h>
#include <stdlib.h>

#define xMAX 1000000000

typedef struct _list{
    int data;
    struct _list *next;
}LIST;
typedef struct _que{
    LIST *head;
    LIST *tail;
}QUE;

int main(){
    int i;
    int n,q;
    scanf("%d %d\n",&n,&q);
    
    QUE Q[n];
    for(i=0;i<n;i++){
        Q[i].head=NULL;
        Q[i].tail=NULL;
    }
    
    LIST *p;
    int com,t,x;
    while(q--){
        scanf("%d %d \n",&com,&t);
        switch(com){
            case 0:
                //pushback
                scanf("%d\n",&x);
                if(Q[t].head==NULL){
                    Q[t].head=(LIST*)malloc(sizeof(LIST));
                    Q[t].head->data=x;
                    Q[t].head->next=NULL;
                    Q[t].tail=Q[t].head;
                }else{
                    Q[t].tail->next=(LIST*)malloc(sizeof(LIST));
                    Q[t].tail=Q[t].tail->next;
                    Q[t].tail->data=x;
                    Q[t].tail->next=NULL;
                }
                break;
            case 1:
                //dump
                if(Q[t].head!=NULL)printf("%d\n",Q[t].head->data);
                break;
            case 2:
                //clear
                if(Q[t].head==NULL)break;
                
                p=Q[t].head;
                if(Q[t].head->next!=NULL){
                    Q[t].head=Q[t].head->next;
                }else{
                    Q[t].head=NULL;
                    Q[t].tail=NULL;
                }
                free(p);
                break;
        }
    }
    
    LIST *tmp;
    for(i=0;i<n;i++){
        if(Q[i].head!=NULL){
            p=Q[i].head;
            while(p!=NULL){
                tmp=p;
                free(p);
                p=tmp->next;
            }
        }
    }
    
    return 0;
}