多线程排序算法 [英] Multi-threading sorting algorithms

问题描述

我必须在Java中为我的算法类实现多线程合并排序和快速排序，并将它们与单线程版本进行比较.但是，我以前从未使用过多线程.

I have to implement a multi threaded Merge Sort and Quick sort in Java for my algorithms class and compare them to my single threaded versions. However, I have never multithreaded before.

是可以多线程处理的代码还是必须重新启动?

Is the code I have able to be multi threaded or do I have to start again?

这是我的单线程算法代码 合并排序. sort()方法是我必须实现的策略模式的一部分.

Here is my code for the single thread algorithms Merge Sort. the sort() method is part of the strategy pattern I have to implement.

    @Override
public int[] sort(int[] list) {
    int array_size = list.length;
    list = msort(list, 0, array_size-1);
    return list;
}

int[] msort(int numbers[], int left, int right) {
    int mid;
    if (left<right) {
        mid = (right + left) / 2;
        msort(numbers, left, mid);
        msort(numbers, mid+1, right);
        merge(numbers, left, mid, mid+1, right);
    }
    return numbers;
}

void merge(int numbers[], int startA, int endA, int startB, int endB) {
    int finalStart = startA;
    int finalEnd = endB;
    int indexC = 0;
    int[] listC = new int[numbers.length];

    while(startA <= endA && startB <= endB){
        if(numbers[startA] < numbers[startB]){
            listC[indexC] = numbers[startA];
            startA = startA+1;
        }
        else{
            listC[indexC] = numbers[startB];
            startB = startB +1;
        }
        indexC++;
    }

    if(startA <= endA){
        for(int i = startA; i < endA; i++){
            listC[indexC]= numbers[i];
            indexC++;
        }
    }

    indexC = 0;
    for(int i = finalStart; i <= finalEnd; i++){
        numbers[i]=listC[indexC];
        indexC++;
    }
}

这是我的快速排序

    @Override
public int[] sort(int[] list) {
    int[] array = quickSort(list, 0, list.length-1);
    return array;
}
int partition(int arr[], int left, int right)
{
      int i = left, j = right;
      int tmp;
      int pivot = arr[(left + right) / 2];

      while (i <= j) {
            while (arr[i] < pivot)
                  i++;
            while (arr[j] > pivot)
                  j--;
            if (i <= j) {
                  tmp = arr[i];
                  arr[i] = arr[j];
                  arr[j] = tmp;
                  i++;
                  j--;
            }
      };

      return i;
}

int[] quickSort(int arr[], int left, int right) {
      int index = partition(arr, left, right);
      if (left < index - 1)
            quickSort(arr, left, index - 1);
      if (index < right)
            quickSort(arr, index, right);
      return arr;
}

干杯！

推荐答案

简短的回答-是的，这些算法可以转换为多线程，而无需从头开始(据我所知).

Short answer - yes, these algorithms can be converted to be multi-threaded without starting from scratch (so far as I can see).

使这些易于"并行化的关键元素是:

The key elements that make these "easy" to parallelize are:

• 每个实现中有两个递归调用
• 这两个递归调用对单独的数据进行操作-它们不应彼此冲突(例如，即使在同一数组中进行操作，它们也将在不同的索引上进行操作)
• 进行两个递归调用的方法要等到两个都完成后才能继续进行
• 这两个呼叫的执行顺序无关紧要

希望能回答您的一些问题.

That's answered some of your questions, hopefully.

更多建议，不确定是否会有用:

Some more advice, not sure how useful this will be:

• 如果将两个递归调用都放入一个新线程中，则当前线程将在等待它们都完成时处于空闲状态
• 当要处理的元素数量很少时，线程的开销可能会比获得的开销高.
• 您可能通常希望限制用于此任务的线程数-您可能希望使用某种形式的线程池或工作队列，并且线程数固定.

这篇关于多线程排序算法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！