Language: Java

import java.util.*;

public class Main {

  static FastScanner sc = new FastScanner();

  public static void main(String[] args) {

    int N = sc.nextInt(); //県の数
    int M = sc.nextInt(); //市の数

    LinkedList<Integer[]>[] prefectures = new LinkedList[N]; //[0] 市の番号 [1] 年
    for (int i = 0; i < N; i++) {
      prefectures[i] = new LinkedList();
    }

    for (int i = 0; i < M; i++) {
      int p = sc.nextInt() - 1;
      int y = sc.nextInt();
      if (prefectures[p].size() == 0) {
        prefectures[p].add(new Integer[]{i, y});
        continue;
      }

      ListIterator<Integer[]> iterator = prefectures[p].listIterator();
      while (iterator.hasNext()) {
        Integer[] pre = iterator.next();
        if (pre[1] > y) {
          iterator.previous();
          iterator.add(new Integer[]{i, y});
          break;
        } else if (!iterator.hasNext()) {
          iterator.add(new Integer[]{i, y});
          break;
        }
      }
    }

    String[] ids = new String[M];
    for (int i = 0; i < N; i++) {
      ListIterator<Integer[]> iterator = prefectures[i].listIterator();
      while(iterator.hasNext()) {
        Integer[] city = iterator.next();
        ids[city[0]] = padding0(i + 1, 6) + padding0(iterator.nextIndex(), 6);
      }
    }

    for (int i = 0; i < M; i++) {
      System.out.println(ids[i]);
    }

  }

  static String padding0(int n, int m) {
    String s = Integer.toString(n);
    while (m - s.length() > 0) s = "0" + s;
    return s;
  }

}

class FastScanner {
  private final InputStream in = System.in;
  private final byte[] buffer = new byte[1024];
  private int ptr = 0;
  private int buflen = 0;
  private boolean hasNextByte() {
    if (ptr < buflen) {
      return true;
    }else{
      ptr = 0;
      try {
        buflen = in.read(buffer);
      } catch (IOException e) {
        e.printStackTrace();
      }
      if (buflen <= 0) {
        return false;
      }
    }
    return true;
  }
  private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
  private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
  private void skipUnprintable() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;}
  public boolean hasNext() { skipUnprintable(); return hasNextByte();}
  public String next() {
    if (!hasNext()) throw new NoSuchElementException();
    StringBuilder sb = new StringBuilder();
    int b = readByte();
    while(isPrintableChar(b)) {
      sb.appendCodePoint(b);
      b = readByte();
    }
    return sb.toString();
  }
  public long nextLong() {
    if (!hasNext()) throw new NoSuchElementException();
    long n = 0;
    boolean minus = false;
    int b = readByte();
    if (b == '-') {
      minus = true;
      b = readByte();
    }
    if (b < '0' || '9' < b) {
      throw new NumberFormatException();
    }
    while(true){
      if ('0' <= b && b <= '9') {
        n *= 10;
        n += b - '0';
      }else if(b == -1 || !isPrintableChar(b)){
        return minus ? -n : n;
      }else{
        throw new NumberFormatException();
      }
      b = readByte();
    }
  }
  public int nextInt() {
    return (int)nextLong();
  }
}

Compiler output:
Main.java:63: error: cannot find symbol
  private final InputStream in = System.in;
                ^
  symbol:   class InputStream
  location: class FastScanner
Main.java:74: error: cannot find symbol
      } catch (IOException e) {
               ^
  symbol:   class IOException
  location: class FastScanner
Note: Main.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
2 errors