YuyuZha0 / y-combinator-java

java version of y-combinator

y-combinator-java

In functional-programing, the Y-Combinartor is defined as :

It is also called Fixed-point combinator:

This is a java version of Y-Combinator.

Usage:

public static void main(String[] args) {
UnaryOperator<Function<Integer, BigInteger>> fib =
    (Function<Integer, BigInteger> f) ->
        (Integer n) -> {
          if (n == 0) return BigInteger.ZERO;
          if (n == 1 || n == 2) return BigInteger.ONE;

          Integer m = n >>> 1;
          if ((n & 1) == 0) {
            BigInteger temp = f.apply(m + 1).add(f.apply(m - 1));
            return f.apply(m).multiply(temp);
          } else {
            BigInteger fm = f.apply(m);
            BigInteger fm1 = f.apply(m + 1);
            return fm.multiply(fm).add(fm1.multiply(fm1));
          }
        };

int n = 1000000;
long t1 = System.nanoTime();
BigInteger n1 = new Y<Integer, BigInteger>().apply(fib).apply(n);
long t2 = System.nanoTime();
BigInteger n2 = new CachedY<Integer, BigInteger>().apply(fib).apply(n);
long t3 = System.nanoTime();
System.out.printf("Y,len:%d,time:%dms%n", n1.toString().length(), (t2 - t1) / 1000_000);
System.out.printf("CachedY,len:%d,time:%dms%n", n2.toString().length(), (t3 - t2) / 1000_000);
}
//Y,len:208988,time:3772ms
//CachedY,len:208988,time:28ms