Library, P64, P66, P100: Replaced Library.sqrt() with BigInteger.sqrt…

…() (Java SE 9+).

Readme: Updated JDK version requirement and copyright year.

Readme.markdown

@@ -7,7 +7,7 @@ Every solved problem has a program written in Java and usually Python. Some solu
 
 All problems from #1 to #100 have a Java and Python program, and problems #1 to #50 have a Mathematica program. This package contains at least 205 solutions in Java, at least 200 in Python, at least 125 in Mathematica, and at least 95 in Haskell.
 
-Java solutions require JDK 8+. Python solutions are tested to work on CPython 3.9.6. Mathematica solutions are tested to work on Mathematica 5.1.
+Java solutions require JDK 9+. Python solutions are tested to work on CPython 3.9.6. Mathematica solutions are tested to work on Mathematica 5.1.
 
 Home page with background info, table of solutions, benchmark timings, and more: [https://www.nayuki.io/page/project-euler-solutions](https://www.nayuki.io/page/project-euler-solutions)
 

java/Library.java

@@ -57,20 +57,6 @@ public static long sqrt(long x) {
 	}
 
 
-	// Returns floor(sqrt(x)), for x >= 0.
-	public static BigInteger sqrt(BigInteger x) {
-		if (x.signum() == -1)
-			throw new IllegalArgumentException("Square root of negative number");
-		BigInteger y = BigInteger.ZERO;
-		for (int i = (x.bitLength() - 1) / 2; i >= 0; i--) {
-			y = y.setBit(i);
-			if (y.multiply(y).compareTo(x) > 0)
-				y = y.clearBit(i);
-		}
-		return y;
-	}
-
-
 	// Tests whether x is a perfect square, for any value x.
 	public static boolean isSquare(int x) {
 		if (x < 0)

java/p064.java

@@ -84,7 +84,7 @@ public QuadraticSurd reciprocal() {
 
 
 		public BigInteger floor() {
-			BigInteger temp = Library.sqrt(b.multiply(b).multiply(d));
+			BigInteger temp = b.multiply(b).multiply(d).sqrt();
 			if (b.signum() == -1)
 				temp = temp.add(BigInteger.ONE).negate();
 			temp = temp.add(a);

java/p066.java

@@ -130,7 +130,7 @@ public QuadraticSurd reciprocal() {
 
 
 		public BigInteger floor() {
-			BigInteger temp = Library.sqrt(b.multiply(b).multiply(d));
+			BigInteger temp = b.multiply(b).multiply(d).sqrt();
 			if (b.signum() == -1)
 				temp = temp.add(BigInteger.ONE).negate();
 			temp = temp.add(a);

java/p100.java

@@ -59,7 +59,7 @@ public String run() {
 		BigInteger y = y0;  // An alias for the number of red discs
 		while (true) {
 			// Check if this solution is acceptable
-			BigInteger sqrt = Library.sqrt(y.multiply(y).multiply(BigInteger.valueOf(8)).add(BigInteger.ONE));
+			BigInteger sqrt = y.multiply(y).multiply(BigInteger.valueOf(8)).add(BigInteger.ONE).sqrt();
 			if (sqrt.testBit(0)) {  // Is odd
 				BigInteger blue = sqrt.add(BigInteger.ONE).divide(BigInteger.valueOf(2)).add(y);
 				if (blue.add(y).compareTo(BigInteger.TEN.pow(12)) > 0)