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_t {
	int x;
	struct node_t* next;
};

int main(void) {
	int n, q;
	struct node_t* stacks[1024];
	int i;
	if (scanf("%d%d", &n, &q) != 2) return 1;
	for (i = 0; i < n; i++) stacks[i] = NULL;
	for (i = 0; i < q; i++) {
		int query, t, x;
		if (scanf("%d%d", &query, &t) != 2) return 1;
		if (query == 0 && scanf("%d", &x) != 1) return 1;
		switch (query) {
			case 0:
				{
					struct node_t* new_node = malloc(sizeof(struct node_t));
					if (new_node == NULL) return 1;
					new_node->x = x;
					new_node->next = stacks[t];
					stacks[t] = new_node;
				}
				break;
			case 1:
				if (stacks[t] == NULL) {
					/* do nothing -> don't do "operation" */
					/* puts("an integer"); */
				} else {
					printf("%d\n", stacks[t]->x);
				}
				break;
			case 2:
				if (stacks[t] != NULL) {
					struct node_t* next = stacks[t]->next;
					free(stacks[t]);
					stacks[t] = next;
				}
				break;
		}
	}
	for (i = 0; i < n; i++) {
		while (stacks[i] != NULL) {
			struct node_t* next = stacks[i]->next;
			free(stacks[i]);
			stacks[i] = next;
		}
	}
	return 0;
}