Data commit

Task/Brilliant-numbers/Java/brilliant-numbers.java

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+import java.util.*;
+
+public class BrilliantNumbers {
+    public static void main(String[] args) {
+        var primesByDigits = getPrimesByDigits(100000000);
+        System.out.println("First 100 brilliant numbers:");
+        List<Integer> brilliantNumbers = new ArrayList<>();
+        for (var primes : primesByDigits) {
+            int n = primes.size();
+            for (int i = 0; i < n; ++i) {
+                int prime1 = primes.get(i);
+                for (int j = i; j < n; ++j) {
+                    int prime2 = primes.get(j);
+                    brilliantNumbers.add(prime1 * prime2);
+                }
+            }
+            if (brilliantNumbers.size() >= 100)
+                break;
+        }
+        Collections.sort(brilliantNumbers);
+        for (int i = 0; i < 100; ++i) {
+            char c = (i + 1) % 10 == 0 ? '\n' : ' ';
+            System.out.printf("%,5d%c", brilliantNumbers.get(i), c);
+        }
+        System.out.println();
+        long power = 10;
+        long count = 0;
+        for (int p = 1; p < 2 * primesByDigits.size(); ++p) {
+            var primes = primesByDigits.get(p / 2);
+            long position = count + 1;
+            long minProduct = 0;
+            int n = primes.size();
+            for (int i = 0; i < n; ++i) {
+                long prime1 = primes.get(i);
+                var primes2 = primes.subList(i, n);
+                int q = (int)((power + prime1 - 1) / prime1);
+                int j = Collections.binarySearch(primes2, q);
+                if (j == n)
+                    continue;
+                if (j < 0)
+                    j = -(j + 1);
+                long prime2 = primes2.get(j);
+                long product = prime1 * prime2;
+                if (minProduct == 0 || product < minProduct)
+                    minProduct = product;
+                position += j;
+                if (prime1 >= prime2)
+                    break;
+            }
+            System.out.printf("First brilliant number >= 10^%d is %,d at position %,d\n",
+                                p, minProduct, position);
+            power *= 10;
+            if (p % 2 == 1) {
+                long size = primes.size();
+                count += size * (size + 1) / 2;
+            }
+        }
+    }
+
+    private static List<List<Integer>> getPrimesByDigits(int limit) {
+        PrimeGenerator primeGen = new PrimeGenerator(100000, 100000);
+        List<List<Integer>> primesByDigits = new ArrayList<>();
+        List<Integer> primes = new ArrayList<>();
+        for (int p = 10; p <= limit; ) {
+            int prime = primeGen.nextPrime();
+            if (prime > p) {
+                primesByDigits.add(primes);
+                primes = new ArrayList<>();
+                p *= 10;
+            }
+            primes.add(prime);
+        }
+        return primesByDigits;
+    }
+}