我需要使用线程递归地根据斐波那契数列中的某个索引找出数字,我尝试了以下代码,但程序永远不会结束。如果我遗漏了什么,请告诉我。
代码:
import java.math.BigInteger;
import java.util.concurrent.*;
public class MultiThreadedFib {
private ExecutorService executorService;
public MultiThreadedFib(final int numberOfThreads) {
executorService = Executors.newFixedThreadPool(numberOfThreads);
}
public BigInteger getFibNumberAtIndex(final int index)
throws InterruptedException, ExecutionException {
Future<BigInteger> indexMinusOne = executorService.submit(
new Callable<BigInteger>() {
public BigInteger call()
throws InterruptedException, ExecutionException {
return getNumber(index - 1);
}
});
Future<BigInteger> indexMinusTwo = executorService.submit(
new Callable<BigInteger>() {
public BigInteger call()
throws InterruptedException, ExecutionException {
return getNumber(index - 2);
}
});
return indexMinusOne.get().add(indexMinusTwo.get());
}
public BigInteger getNumber(final int index)
throws InterruptedException, ExecutionException {
if (index == 0 || index == 1)
return BigInteger.valueOf(index);
return getFibNumberAtIndex(index - 1).add(getFibNumberAtIndex(index - 2));
}
}
修复它(感谢Fiver)
我不是从 call 方法调用 getNumber(int) ,而是调用一个动态编程算法来计算该索引处的数字。
代码是:
public class DynamicFib implements IFib {
private Map<Integer, BigInteger> memoize = new HashMap<Integer, BigInteger>();
public DynamicFib() {
memoize.put(0, BigInteger.ZERO);
memoize.put(1, BigInteger.ONE);
}
public BigInteger getFibNumberAtIndex(final int index) {
if (!memoize.containsKey(index))
memoize.put(index, getFibNumberAtIndex(index - 1).add(getFibNumberAtIndex(index - 2)));
return memoize.get(index);
}
}