java用流替换for循环中的递归
我很难用Stream
替换包含递归调用的for循环。代码是关于在已知给定数的素数因子时生成该数的适当因子。该算法取自here,在图像中对其进行了描述。这是我的代码的一部分,用于演示,可以运行:
public class Demo {
private static void generateDivisorsTraditional(int start, long lastFactor, Multiset<Long> primeFactors, Set<Long> divisors) {
for (int i = start; i < primeFactors.elementSet().size(); i++) {
long prime = Iterables.get(primeFactors.elementSet(), i);
int count = primeFactors.count(prime);
++start;
for (int c = 0; c <= count; c++) {
long factor = ArithmeticUtils.pow(prime, c);
divisors.add(lastFactor * factor);
generateDivisorsTraditional(start, lastFactor * factor, primeFactors, divisors);
}
}
}
private static void generateDivisorsStream(int start, long lastFactor, Multiset<Long> primeFactors, Set<Long> divisors) {
IntStream.range(start, primeFactors.elementSet().size())
.forEach((int i) -> {
long prime = Iterables.get(primeFactors.elementSet(), i);
int count = primeFactors.count(prime);
final int begin = start + 1;
IntStream.range(0, count + 1)
.forEach((int c) -> {
long factor = ArithmeticUtils.pow(prime, c);
divisors.add(lastFactor * factor);
generateDivisorsStream(begin, lastFactor * factor, primeFactors, divisors);
});
});
}
private static void testTraditional(Multiset<Long> primeFactors) {
Set<Long> divisors = new TreeSet<>();
generateDivisorsTraditional(0, 1, primeFactors, divisors);
System.out.println("Traditional=> " + divisors);
}
private static void testStream(Multiset<Long> primeFactors) {
Set<Long> divisors = new TreeSet<>();
generateDivisorsStream(0, 1, primeFactors, divisors);
System.out.println("Stream=> " + divisors);
}
private static void testStream1(Multiset<Long> primeFactors) {
Set<Long> divisors = new TreeSet<>();
new Inner().generateDivisorsStream(1, primeFactors, divisors);
System.out.println("Stream1=> " + divisors);
}
public static void main(String[] args) {
System.out.println("Test number: 10");
Multiset<Long> primeFactors = TreeMultiset.create();
primeFactors.add(2L);
primeFactors.add(5L);
testTraditional(primeFactors);
testStream(primeFactors);
testStream1(primeFactors);
System.out.println();
System.out.println("Test number: 90");
primeFactors = TreeMultiset.create();
primeFactors.add(2L);
primeFactors.add(3L);
primeFactors.add(3L);
primeFactors.add(5L);
testTraditional(primeFactors);
testStream(primeFactors);
testStream1(primeFactors);
}
private static class Inner {
private int start = 0;
private void generateDivisorsStream(long lastFactor, Multiset<Long> primeFactors, Set<Long> divisors) {
IntStream.range(start, primeFactors.elementSet().size())
.forEach((int i) -> {
long prime = Iterables.get(primeFactors.elementSet(), i);
int count = primeFactors.count(prime);
++start;
IntStream.range(0, count + 1)
.forEach((int c) -> {
long factor = ArithmeticUtils.pow(prime, c);
divisors.add(lastFactor * factor);
generateDivisorsStream(lastFactor * factor, primeFactors, divisors);
});
});
}
}
}
它生成的输出是:
Test number: 10
Traditional=> [1, 2, 5, 10]
Stream=> [1, 2, 5, 10, 25]
Stream1=> [1, 2, 5]
Test number: 90
Traditional=> [1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90]
Stream=> [1, 2, 3, 5, 6, 9, 10, 15, 18, 25, 27, 30, 45, 50, 75, 81, 90, 125, 135, 225, 405]
Stream1=> [1, 2, 3, 5, 9]
顾名思义,方法generateDivisorsTraditional
使用传统的for循环,其中我对同一方法进行了递归调用。方法generateDivisorsStream
使用IntStream.range()
模拟for循环
我怀疑{generateDivisorsTraditional
中使用final int begin = start + 1;
而不是++start;
,并发现它已开始生成错误的结果。我在内部类Inner
中还有另一个变量,它也产生了错误的输出
我想知道为什么这不是它应该表现的方式?我犯了什么错误
# 1 楼答案
我认为有一些错误:
它打印: