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Ricorsione doppia esempio serie di fibonacci

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This commit is contained in:
Fabio Scotto di Santolo
2020-01-25 11:25:37 +01:00
parent 6934725179
commit d61c649e16
1 changed files with 22 additions and 0 deletions
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22
functional-programming-java/src/main/java/org/gym/fp/fpjava/demo/RecursionDemo.java
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@@ -1,14 +1,20 @@
package org.gym.fp.fpjava.demo; package org.gym.fp.fpjava.demo;
import lombok.AccessLevel;
import lombok.NoArgsConstructor;
import org.gym.fp.fpjava.type.TailCall; import org.gym.fp.fpjava.type.TailCall;
import java.math.BigInteger;
import static org.gym.fp.fpjava.type.TailCall.ret; import static org.gym.fp.fpjava.type.TailCall.ret;
import static org.gym.fp.fpjava.type.TailCall.suspend; import static org.gym.fp.fpjava.type.TailCall.suspend;
@NoArgsConstructor(access = AccessLevel.PRIVATE)
public class RecursionDemo { public class RecursionDemo {
public static void run() { public static void run() {
System.out.println(add(10, 1000)); System.out.println(add(10, 1000));
System.out.print(fibonacci(10000));
} }
public static int add(int x, int y) { public static int add(int x, int y) {
@@ -20,4 +26,20 @@ public class RecursionDemo {
? ret(x) ? ret(x)
: suspend(() -> addRec(x + 1, y - 1)); : suspend(() -> addRec(x + 1, y - 1));
} }
// ES. 4.1, 4.2
public static BigInteger fibonacci(int number) {
class Aux {
public TailCall<BigInteger> fib(BigInteger acc1, BigInteger acc2, BigInteger x) {
if (x.equals(BigInteger.ZERO)) {
return ret(BigInteger.ZERO);
} else if (x.equals(BigInteger.ONE)) {
return ret(acc1.add(acc2));
} else {
return suspend(() -> fib(acc2, acc1.add(acc2), x.subtract(BigInteger.ONE)));
}
}
}
return (new Aux()).fib(BigInteger.ONE, BigInteger.ZERO, BigInteger.valueOf(number)).eval();
}
} }