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Q10845.java
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Q10845.java
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package forRank;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.StringTokenizer;
public class Q10845 {
private static class Node <T>{
T value;
Node<T> next;
public Node(T value){
this.value = value;
next = null;
}
}
private static class Queue <T>{
Node<T> front;
Node<T> back;
int size;
public Queue(){
front = null;
back = null;
size = 0;
}
public void push(T value){
Node<T> newNode = new Node<T>(value);
if(back == null){ //or front == null
back = front = newNode;
} else {
back.next = newNode;
back = newNode;
}
size++;
}
public T pop(){
Node<T> curNode = front;
if(front != null){
if(front.next == null)
back = front = null;
else
front = front.next;
size--;
return curNode.value;
}
return null;
}
public int getSize(){
return size;
}
public boolean isEmpty(){
return (front == null); //or back == null
}
public T getFront(){
if(front == null)
return null;
return front.value;
}
public T getBack(){
if(back == null)
return null;
return back.value;
}
}
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
int n = Integer.parseInt(br.readLine());
Queue<Integer> queue = new Queue<Integer>();
for (int i = 0; i < n; i++) {
StringTokenizer st = new StringTokenizer(br.readLine());
String command = st.nextToken();
if(command.equals("push")){
int value = Integer.parseInt(st.nextToken());
queue.push(value);
} else if(command.equals("pop")){
Object rs = queue.pop();
if (rs == null)
bw.write("-1\n");
else
bw.write(rs + "\n");;
} else if(command.equals("size")){
bw.write(queue.getSize() + "\n");
} else if(command.equals("empty")){
if(queue.isEmpty())
bw.write("1\n");
else
bw.write("0\n");
} else if(command.equals("front")){
Object rs = queue.getFront();
if( rs == null )
bw.write("-1\n");
else
bw.write(rs + "\n");
} else if(command.equals("back")){
Object rs = queue.getBack();
if( rs == null )
bw.write("-1\n");
else
bw.write(rs + "\n");
}
}
br.close();
bw.close();
}
}