面试代码

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一，两个线程交替打印

public class TwoThreadPrint {                                                                                 public static class Printer {                                                                                 private Boolean flag = false;                                                                             public synchronized void printA() {                                                                           try {                                                                                                         while (!flag) {                                                                                               wait();                                                                                               }                                                                                                         System.out.println(Thread.currentThread().getName() + " ---- A");                                         flag = !flag;                                                                                             notify();                                                                                             } catch (InterruptedException e) {                                                                            e.printStackTrace();                                                                                  }                                                                                                     }                                                                                                         public synchronized void printB() {                                                                           try {                                                                                                         while (flag) {                                                                                                wait();                                                                                               }                                                                                                         System.out.println(Thread.currentThread().getName() + " ---- B");                                         flag = !flag;                                                                                             notify();                                                                                             } catch (InterruptedException e) {                                                                            e.printStackTrace();                                                                                  }                                                                                                     }                                                                                                     }                                                                                                         public static class ThreadA extends Thread {                                                                  private Printer printer;                                                                                  public ThreadA(Printer printer) {                                                                             this.printer = printer;                                                                               }                                                                                                         @Override                                                                                                 public void run() {                                                                                           for (int i = 0; i < 10; i++) {                                                                                this.printer.printA();                                                                                }                                                                                                     }                                                                                                     }                                                                                                         public static class ThreadB extends Thread {                                                                  private Printer printer;                                                                                  public ThreadB(Printer printer) {                                                                             this.printer = printer;                                                                               }                                                                                                         @Override                                                                                                 public void run() {                                                                                           for (int i = 0; i < 10; i++) {                                                                                this.printer.printB();                                                                                }                                                                                                     }                                                                                                     }                                                                                                         public static void main(String[] args) throws Exception {                                                     Printer printer = new Printer();                                                                          Thread threadA = new ThreadA(printer);                                                                    Thread threadB = new ThreadB(printer);                                                                    threadA.start();                                                                                          threadB.start();                                                                                      }                                                                                                     }

二，给定一个能够生成均匀1~5随机枚举数的函数，请设计一个能够生成均匀1~7随机枚举数的函数。参考这里

public class Rand57 {                                                                              private static Random random = new Random();                                                   public static int rand5() {                                                                        return random.nextInt(5);                                                                  }                                                                                              private static int[][] initArray = new int[5][5];                                              public static int rand7() {                                                                        int col = Rand57.rand5();                                                                      int row = Rand57.rand5();                                                                      if (col == 4 && row > 0) {                                                                         return Rand57.rand7();                                                                     } else {                                                                                           return Rand57.initArray[col][row] % 7;                                                     }                                                                                          }                                                                                              static {                                                                                           int val = 0;                                                                                   for (int i = 0; i < 5; i++) {                                                                      for (int j = 0; j < 5; j++) {                                                                      Rand57.initArray[i][j] = (val % 7);                                                            val++;                                                                                     }                                                                                          }                                                                                          }                                                                                              public static void main(String[] args) throws Exception {                                          System.out.println(Rand57.rand7());                                                            Map<String, Integer> resultMap = new HashMap<String, Integer>();                               for (int i = 0; i < 10000000; i++) {                                                               String val = String.valueOf(Rand57.rand7());                                                   if (null == resultMap.get(val)) {                                                                  resultMap.put(val, 1);                                                                     } else {                                                                                           resultMap.put(val, resultMap.get(val).intValue() + 1);                                     }                                                                                          }                                                                                              for (String key : resultMap.keySet()) {                                                            System.out.println(key + "----" + resultMap.get(key));                                     }                                                                                          }                                                                                          }

三，对指定的N个数字排序

public class SortRandomNumber {    public static void main(String[] args) throws Exception {        File file = new File("random_number.txt");        BufferedReader br = new BufferedReader(new FileReader(file));        long start = System.currentTimeMillis();        byte[] location = new byte[10000000];        for (int i = 0; i < location.length; i++) {            location[i] = 0;        }        File outFile = new File("sort_number.txt");        outFile.createNewFile();        BufferedWriter bw = new BufferedWriter(new FileWriter(outFile));        String line = br.readLine();        while (StringUtils.isNotBlank(line)) {            location[Integer.valueOf(line)] = 1;            line = br.readLine();        }        boolean first = true;        for (int i = 0; i < location.length; i++) {            if (location[i] == 1) {                if (!first) {                    bw.newLine();                }                bw.write(String.valueOf(i));                first = false;            }        }        long end = System.currentTimeMillis();        System.out.println("total time: " + (end -start));        br.close();        bw.flush();        bw.close();    }}

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