有人可以给我一个链接或向我提供多线程合并排序的java代码吗?
优先使用遗嘱执行人的人!
非常感谢!
答案 0 :(得分:6)
这是我使用2个线程的MergeSort版本,它可以轻松扩展到n个线程(只需将原始数组拆分为n个子数组)。对于1000万个数字,它比单线程对应的速度快25%左右。
import java.util.Random;
public class MergeSortThreaded {
public static void finalMerge(int[] a, int[] b) {
int[] result = new int[a.length + b.length];
int i=0;
int j=0;
int r=0;
while (i < a.length && j < b.length) {
if (a[i] <= b[j]) {
result[r]=a[i];
i++;
r++;
} else {
result[r]=b[j];
j++;
r++;
}
if (i==a.length) {
while (j<b.length) {
result[r]=b[j];
r++;
j++;
}
}
if (j==b.length) {
while (i<a.length) {
result[r]=a[i];
r++;
i++;
}
}
}
}
public static void main(String[] args) throws InterruptedException {
Random rand = new Random();
int[] original = new int[10000000];
for (int i=0; i<original.length; i++) {
original[i] = rand.nextInt(1000);
}
long startTime = System.currentTimeMillis();
int[] subArr1 = new int[original.length/2];
int[] subArr2 = new int[original.length - original.length/2];
System.arraycopy(original, 0, subArr1, 0, original.length/2);
System.arraycopy(original, original.length/2, subArr2, 0, original.length - original.length/2);
Worker runner1 = new Worker(subArr1);
Worker runner2 = new Worker(subArr2);
runner1.start();
runner2.start();
runner1.join();
runner2.join();
finalMerge (runner1.getInternal(), runner2.getInternal());
long stopTime = System.currentTimeMillis();
long elapsedTime = stopTime - startTime;
System.out.println("2-thread MergeSort takes: " + (float)elapsedTime/1000 + " seconds");
}
}
class Worker extends Thread {
private int[] internal;
public int[] getInternal() {
return internal;
}
public void mergeSort(int[] array) {
if (array.length > 1) {
int[] left = leftHalf(array);
int[] right = rightHalf(array);
mergeSort(left);
mergeSort(right);
merge(array, left, right);
}
}
public int[] leftHalf(int[] array) {
int size1 = array.length / 2;
int[] left = new int[size1];
for (int i = 0; i < size1; i++) {
left[i] = array[i];
}
return left;
}
public int[] rightHalf(int[] array) {
int size1 = array.length / 2;
int size2 = array.length - size1;
int[] right = new int[size2];
for (int i = 0; i < size2; i++) {
right[i] = array[i + size1];
}
return right;
}
public void merge(int[] result, int[] left, int[] right) {
int i1 = 0;
int i2 = 0;
for (int i = 0; i < result.length; i++) {
if (i2 >= right.length || (i1 < left.length && left[i1] <= right[i2])) {
result[i] = left[i1];
i1++;
} else {
result[i] = right[i2];
i2++;
}
}
}
Worker(int[] arr) {
internal = arr;
}
public void run() {
mergeSort(internal);
}
}
答案 1 :(得分:3)
我建议多线程mergesort与常规mergesort非常相似,但是,当递归调用列表的每一半的mergesort时,设置算法以调用新Thread中的每个合并。然后,您可以等待两个线程完成,然后将两个列表合并在一起,然后返回。简单!
您在问题中表示要使用Executor
- 我建议使用java.util.concurrent
包,尤其是Future
界面。
<强>资源:强>
答案 2 :(得分:2)
我尝试使用join方法。它基本上为每个子问题生成线程,并等待使用join完成生成的线程。
让我知道你的意见。
package com.kayan.dsAlgo;
public class MergeSorter implements Runnable{
private int[] arr;
private int Size;
private int left;
private int right;
private int[] resultArr ;
public MergeSorter(int[] arr, int i, int j) {
this.arr = arr;
this.Size = arr.length;
//this.resultArr = new int[j-i+1];
this.left = i;
this.right = j;
}
@Override
public void run() {
System.out.println("Starting new thread left :"+this.left+" right "+this.right);
sort();
}
public static void main(String[] args) {
int arr[] ={3,6,4,2,1,10} ;
MergeSorter mr = new MergeSorter(arr,0,arr.length-1);
Thread t = new Thread(mr);
t.start();
//mr.run();
try {
t.join();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
for (int i :mr.resultArr)
System.out.print(i+" ");
//int res[]= mr.sort(0,arr.length-1);
}
private void sort() {
if(left==right && left >=0 )
{
this.resultArr = new int[]{arr[left]};
return;
}
if(left>right) return;
int rightLimit = this.left+(right-left)/2;
//int leftArr[] = sort( left,rightLimit );
MergeSorter mleft = new MergeSorter(arr,left,rightLimit);
Thread t1 = new Thread(mleft);
t1.start();
int leftlimit = 1 + rightLimit;
//int rightArr[] = sort(leftlimit , right);
MergeSorter mright= new MergeSorter(arr,leftlimit,right);
Thread t2 = new Thread(mright);
t2.start();
try {
t1.join();
t2.join();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
merge(mleft.resultArr,mright.resultArr);
}
private int[] merge(int[] left, int[] right) {
resultArr = new int[left.length+right.length];
int r=0;
int i=0;
int j=0;
while(i<left.length && j <right.length )
{
if( i<left.length && j<right.length && left[i] < right[j] )
resultArr[r++] = left[i++];
else if( j<right.length && i<left.length && right[j] < left[i])
resultArr[r++] = right[j++];
}
while(i<left.length)
{
resultArr[r++] = left[i++];
}
while(j<right.length)
{
resultArr[r++] = right[j++];
}
//System.out.println("resultArr "+resultArr);
return resultArr;
}
}
答案 3 :(得分:0)
以下是使用Java7 ForkJoin框架的示例: http://www.ibm.com/developerworks/java/library/j-jtp03048.html
您可以在此处使用测试版在Java6中使用此框架: http://gee.cs.oswego.edu/dl/concurrency-interest/