從一億條數據中取出top100

import java.util.Random;
import java.util.TreeSet;

public class Top100
{
    public static void main(String[] args)
    {
        long begin = System.currentTimeMillis();
        int[] numarray = new int[100000000];
        Random random = new Random();
        for (int i = 0; i < numarray.length; ++i)
        {
            numarray[i] = random.nextInt(numarray.length);
        }

    long middle = System.currentTimeMillis();
    TreeSet<Integer> top = new TreeSet<Integer>();
    for (int i = 0; i < numarray.length; ++i)
    {
        if (top.size() < 100)
        {
            top.add(numarray[i]);
            continue;
        }

        if (numarray[i] > top.first())
        {
            top.pollFirst();
            top.add(numarray[i]);
        }
    }

    long end = System.currentTimeMillis();
    // System.out.println(top);
    System.out.printf("排序用時:%d\n總共用時:%d\n", end - middle, end - begin);
}

}</pre>
運行時可能內存溢出,可使用下面命令執行:

java -Xms128M -Xmx768M Top100