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记录《编程珠玑》中通过位开关来实现排序的方法

 
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程序实现自动生成1000万个从1000万到1亿之间的随机数写入到文件中,然后对这些数进行从小到大排序写入到新的文件中。

核心思想:用一个很大的数组来记录随机数出现的次数,然后直接输出这个基数器的序号即为排序结果。

	private static final int SIZE = 10000000;//随机数数量
	private static final int START = 10000000;//随机数开始值
	private static final int END = 89999999;//随机数增量
	
	private static final String DIR = "e:/test/";

	public static void main(String[] args) throws Exception{
		long time  = System.currentTimeMillis();
		createTestData();
		System.out.println("耗时:"+(System.currentTimeMillis() - time));
		time  = System.currentTimeMillis();
		sort();
		System.out.println("耗时:"+(System.currentTimeMillis() - time));
		System.out.println("完成!");
	}
	
	private static void sort()throws Exception{
		System.out.println("初始化排序数组...");
		int[] record = new int[END+1];
		for(int i = 0;i<record.length;i++){
			record[i] = 0;
		}
		File file = new File(DIR+"test.txt");
		BufferedReader br = new BufferedReader(new FileReader(file));
		String line;
		while((line = br.readLine())!=null){
			record[Integer.parseInt(line) - START] += 1; 
		}
		br.close();
		
		System.out.println("正在排序...");
		File file2 = new File(DIR+"test-result.txt");
		if(!file.exists()){
			file.createNewFile();
		}
		BufferedWriter bw = new BufferedWriter(new FileWriter(file2,true));
		int i = START;
		for(int r : record){
			if(r>=1){
				for(int j = r;j>0;j--){
					bw.write(i+(r>1?" <---":""));
					bw.newLine();
				}
			}
			i++;
			//System.out.println("i="+i);
		}
		bw.close();
	}
	
	private static void createTestData()throws Exception{
		Random r = new Random();
		File file = new File(DIR+"test.txt");
		if(!file.exists()){
			file.createNewFile();
		}
		System.out.println("正在生成随机数...");
		BufferedWriter bw = new BufferedWriter(new FileWriter(file,true));
		for(int i = 0;i<SIZE;i++){
			bw.write(START+r.nextInt(END)+"");
			bw.newLine();
			//System.out.println("i="+i);
		}
		bw.close();
	}


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