Problem:
Stack

Stack is a container of elements that are inserted and deleted according to LIFO (Last In First Out).

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

push($t$, $x$): Insert an integer $x$ to $S_t$.

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

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

In the initial state, all stacks 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 push, top and pop operations respectively.

Output

For each top 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

3
5
2

Solution in C (judge verdict: Accepted)

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

struct node
{
    int ele;
    struct node *next;
};

struct stack
{
    struct node *top;
};

typedef struct node * Node;
typedef struct stack * Stack;

void initialize(Stack *);
void push(Stack, int);
void top(Stack);
void pop(Stack);

int main(void)
{
    int n, q, i;
    int cmd, idx, val;

    scanf("%d %d", &n, &q);

    Stack *list = (Stack *) malloc(sizeof(Stack *) * n);
    for (i = 0; i < n; i++)
        initialize(list + i);
    
    for (i = 0; i < q; i++) {
        scanf("%d %d", &cmd, &idx);
        if (cmd == 0) {
            scanf("%d", &val);
            push(list[idx], val);
        } else if (cmd == 1) {
            top(list[idx]);
        } else if (cmd == 2) {
            pop(list[idx]);
        }
    }

    return 0;
}

void initialize(Stack *s)
{
    (*s) = (Stack) malloc(sizeof(struct stack));
    (*s)->top = NULL;
}

void push(Stack s, int x)
{
    Node tmp = (Node) malloc(sizeof(struct node));
    tmp->ele = x;
    tmp->next = s->top;
    s->top = tmp;
}

void top(Stack s)
{
    if (s->top)
        printf("%d\n", s->top->ele);
}

void pop(Stack s)
{
    if (s->top) {
        Node tmp = s->top;
        s->top = s->top->next;
        free(tmp);
    }
}