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Stacks.java
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Stacks.java
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import java.io.*;
import java.util.*;
public class Stacks {
public static void main(String[] args) throws IOException {
BufferedReader f = new BufferedReader(new InputStreamReader(System.in));
int n = Integer.parseInt(f.readLine());
Stack<Integer>[] stacks = (Stack<Integer>[]) new Stack[1000];
for (int i = 0; i < 1000; i++) {
stacks[i] = new Stack<Integer>();
}
while (n-- > 0) {
StringTokenizer st = new StringTokenizer(f.readLine());
String op = st.nextToken();
if (op.equals("PUSH")) {
stacks[Integer.parseInt(st.nextToken()) - 1].push(Integer.parseInt(st.nextToken()));
}
else {
System.out.println(stacks[Integer.parseInt(st.nextToken()) - 1].pop());
}
}
f.close();
System.exit(0);
}
}
class Stack<Item> implements Iterable<Item> {
private Node first; // top of stack
private int N;
private class Node { // nested class to define nodes
Item item;
Node next;
}
public boolean isEmpty() {
return N == 0;
}
public int size() {
return N;
}
public void push(Item item) {
// Add item to top of the stack.
Node oldFirst = first;
first = new Node();
first.item = item;
first.next = oldFirst;
N++;
}
public Item pop() {
// Remove the item from the top of the stack.
Item item = first.item;
first = first.next;
N--;
return item;
}
public Item peek() {
return first.item;
}
public Iterator<Item> iterator() {
return new ListIterator();
}
private class ListIterator implements Iterator<Item> {
private Node current = first;
public boolean hasNext() {
return current != null;
}
public void remove() {}
public Item next() {
Item item = current.item;
current = current.next;
return item;
}
}
}