求999的阶乘！！！！
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- Java code
protected static ArrayList<BigInteger> list = new ArrayList<BigInteger>(); static { list.add(BigInteger.valueOf(1)); } public static BigInteger factorial(int x) { for (int size = list.size(); size <= x; size++) { BigInteger lastfact = (BigInteger) list.get(size - 1); BigInteger nextfact = lastfact.multiply(BigInteger.valueOf(size)); list.add(nextfact); } return (BigInteger)list.get(x); } public static void main(String[] args) { System.out.println(999 + "!=" + factorial(6)); }
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- Java code
public final class Factorial { /** * Default thread count(CPU count * 4) */ static final int THREAD_COUNT; static { THREAD_COUNT = Runtime.getRuntime().availableProcessors() << 2; } /** * Never instantiate this class. */ private Factorial() { } /** * Calculates the factorial of n. A new thread pool will be initialized to * perform the calculation task, and destroyed thereafter. * * @param n * the value of n * @return the factorial of the given n * @throws Exception * if exception occurs */ public static final BigInteger factorial(final int n) throws Exception { ExecutorService threadPool = Executors.newFixedThreadPool(THREAD_COUNT); try { return factorial(n, threadPool, THREAD_COUNT); } finally { threadPool.shutdown(); } } /** * Calculates the factorial of n. A specified thread pool will be used to * perform the calculation task, and will not be automatically destroyed. * * @param n * the value of n * @param threadPool * the given thread pool to perform the calculation task * @param threadCount * the number of threads to perform the calculation task * @return the factorial of the given n * @throws Exception * if exception occurs */ public static BigInteger factorial(final int n, ExecutorService threadPool, final int threadCount) throws Exception { List<Callable<BigInteger>> tasks = new ArrayList<Callable<BigInteger>>(threadCount); for (int i = 1; i <= threadCount; i++) { final int threadNo = i; Callable<BigInteger> worker = new Callable<BigInteger>() { @Override public BigInteger call() throws Exception { BigInteger result = BigInteger.ONE; for (int x = threadNo; x <= n; x += threadCount) { result = BigInteger.valueOf(x).multiply(result); } return result; } }; tasks.add(worker); } BigInteger result = BigInteger.ONE; List<Future<BigInteger>> futureList = threadPool.invokeAll(tasks); for (Future<BigInteger> future : futureList) { result = future.get().multiply(result); } return result; }}
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- Java code
import java.math.BigInteger;public class Test { public static void main(String args[]) { BigInteger bi = factorial(999); System.out.println(bi); } public static BigInteger factorial(int n) { if(n < 2) { return BigInteger.ONE; } int[] oddCount = new int[Integer.numberOfTrailingZeros(Integer.highestOneBit(n))]; int shift = init(oddCount, n); BigInteger result = BigInteger.ONE; BigInteger bg = BigInteger.ONE; BigInteger tmp = BigInteger.ONE; int max = oddCount[oddCount.length - 1]; int offset = (oddCount[0] + 1) & 1; int oddStart = 1; while(oddStart <= max) { tmp = tmp.multiply(new BigInteger(String.valueOf(2 * oddStart + 1))); if(oddCount[offset] == oddStart) { offset++; bg = bg.multiply(tmp); tmp = BigInteger.ONE; result = result.multiply(bg); } oddStart++; } return result.shiftLeft(shift); }}