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import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.Random;
import java.lang.Math;
import java.util.List;
import java.util.ArrayList;
public class DivideConquer{
private static int partion(int[] nums, int left, int right){
int num = nums[left];
int i = left + 1, j = right;
while(i <= j){
while(i <= j && nums[i] >= num){
i++;
}
while(i <= j && nums[j] < num){
j--;
}
if(i < j){
int temp = nums[j];
nums[j] = nums[i];
nums[i] = temp;
}
}
int temp = nums[j];
nums[j] = num;
nums[left] = temp;
return j;
}
public static void sort(int[] nums, int left, int right, int k){
if(right <= left){
return;
}
int mid = DivideConquer.partion(nums, left, right);
int num = mid - left + 1;
if(num == k){
return;
}
else if(num > k){
DivideConquer.sort(nums, left, mid - 1, k);
}
else{
DivideConquer.sort(nums, mid + 1, right, k - num);
}
}
public static int[] divideConquer(int[] nums, int m, int k){
int n = nums.length / m;
ExecutorService executor = Executors.newFixedThreadPool(m);
List<Future<int[]>> futureList = new ArrayList<>();
for(int i = 0; i < m; i++){
int[] partNums = new int[n];
for(int j = 0; j < n; j++){
partNums[j] = nums[i * n + j];
}
futureList.add(executor.submit(new ProcessThread(partNums, k)));
}
executor.shutdown();
int[] topkMerge = new int[m * k];
int index = 0;
for(Future<int[]> future: futureList){
try{
int[] container = future.get();
for(int i = 0; i < container.length; i++){
topkMerge[index * k + i] = container[i];
}
index += 1;
}catch(Exception e){
e.printStackTrace();
}
}
DivideConquer.sort(topkMerge, 0, topkMerge.length - 1, k);
int[] res = new int[k];
for(int j = 0; j < k; j++){
res[j] = topkMerge[j];
}
return res;
}
public static int[] generateNums(int N, int highBound){
int[] nums = new int[N];
Random random = new Random();
for(int i = 0; i < N; i++){
nums[i] = random.nextInt(highBound);
}
return nums;
}
public static void printArray(int[] nums, String title){
System.out.println("------------" + title + "-----------------------\n");
for(int i = 0; i < nums.length; i++){
System.out.print(nums[i]);
if((i + 1) % 10 == 0){
System.out.println();
}
else{
System.out.print("\t");
}
}
System.out.println("\n-----------------------------------");
}
public static double experience(int[] nums, int m, int k, int N){
double time = 0.0;
for(int epoch = 0; epoch < N; epoch++){
long startTime = System.currentTimeMillis();
int[] result = DivideConquer.divideConquer(nums, m, k);
long endTime = System.currentTimeMillis();
time += (endTime - startTime) / 1000.0;
}
return time / N;
}
public static void main(String[] args){
int[] nums = DivideConquer.generateNums(1000000, 101);
double averageTime = DivideConquer.experience(nums, 10, 100, 10);
System.out.println("程序运行平均时间：" + Math.round(averageTime * 1000) + "ms");
}
}
class ProcessThread implements Callable<int[]> {
private int[] nums;
private int k;
public ProcessThread(int[] nums, int k){
this.nums = nums;
this.k = k;
}
private int partion(int left, int right){
int num = nums[left];
int i = left + 1, j = right;
while(i <= j){
while(i <= j && nums[i] >= num){
i++;
}
while(i <= j && nums[j] < num){
j--;
}
if(i < j){
int temp = nums[j];
nums[j] = nums[i];
nums[i] = temp;
}
}
int temp = nums[j];
nums[j] = num;
nums[left] = temp;
return j;
}
private void sort(int left, int right){
if(right <= left){
return;
}
int mid = partion(left, right);
int num = mid - left + 1;
if(num == k){
return;
}
else if(num > k){
sort(left, mid - 1);
}
else{
sort(mid + 1, right);
}
}
@Override
public int[] call(){
try{
sort(0, nums.length - 1);
int[] container = new int[k];
for(int i = 0; i < k; i++){
container[i] = nums[i];
}
return container;
}catch(Exception e){
e.printStackTrace();
return null;
}
}
}
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