69 lines
2 KiB
Java
69 lines
2 KiB
Java
package insert_digit_anywhere_prime;
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import java.util.HashMap;
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import java.util.Iterator;
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import java.util.stream.IntStream;
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import java.util.ArrayList;
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class Util
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{
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private static HashMap<Long, Boolean> primes;
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private static HashMap<Long, Boolean> squareFree;
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public static void init()
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{
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primes = new HashMap<Long, Boolean>();
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squareFree = new HashMap<Long, Boolean>();
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}
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public static boolean isPrime(long val)
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{
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// Add 2 to the HashMap in advance in order to quickly exclude even number later
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primes.put(2l, true);
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if (primes.containsKey(val)) {
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return primes.get(val);
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}
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if (val < 2) {
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primes.put(val, false);
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return false;
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}
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/* I tried to make this process more readable but I'm not sure about the efficiency
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* TODO check the efficiency of this new method
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*/
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boolean temp = (val % 2) != 0
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&&
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IntStream.rangeClosed(3, (int) Math.sqrt(val))
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.filter(n -> n % 2 != 0)
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.noneMatch(n -> (val % n == 0));
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primes.put(val, temp);
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return temp;
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}
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public static boolean isSquareFree(long val)
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{
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if (squareFree.containsKey(val)) {
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return squareFree.get(val);
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}
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for (int i = 2; i * i <= val; i++) {
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if (isPrime(i)) {
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if (val % (i * i) == 0) {
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squareFree.put(val, false);
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return false;
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}
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}
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}
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squareFree.put(val, true);
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return true;
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}
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// Did some cleaning to this util method
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public static void printList(ArrayList<Long> ls)
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{
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Iterator<Long> it = ls.iterator();
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System.out.printf("[%s",it.next());
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do{
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System.out.printf(", %s", it.next());
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}while(it.hasNext());
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System.out.print("]\n");
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}
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}
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