lc: add solution for finding closest prime numbers in a range

Author: electyrion

src/main/java/com/thealgorithms/leetcode/ClosestPrimeNumbersInRange.java

@@ -0,0 +1,70 @@
+package com.thealgorithms.leetcode;
+
+import java.util.Arrays;
+
+public class ClosestPrimeNumbersInRange {
+    public int[] closestPrimes(int left, int right) {
+        // get all primes up to right
+        boolean[] isPrime = sieveOfEratosthenes(right);
+        
+        // first two primes in range
+        int first = -1;
+        int second = -1;
+        
+        int minDiff = Integer.MAX_VALUE;
+        int prev = -1;
+        
+        for (int i = Math.max(2, left); i <= right; i++) {
+            if (isPrime[i]) {
+                if (prev == -1) {
+                    prev = i;
+                } else {
+                    int diff = i - prev;
+                    if (diff < minDiff) {
+                        minDiff = diff;
+                        first = prev;
+                        second = i;
+                    }
+                    prev = i;
+                }
+            }
+        }
+        
+        return first == -1 ? new int[]{-1, -1} : new int[]{first, second};
+    }
+
+    public boolean isPrime(int n) {
+        if (n <= 1) return false;
+        if (n <= 3) return true;
+        if (n % 2 == 0 || n % 3 == 0) return false;
+
+        // check for prime by testing divisors up to square root of n, can skip even numbers
+        // and optimize by checking only numbers of form 6k + 1
+        for (int i = 5; i * i <= n; i+= 6) {
+            if (n % i == 0 || n % (i + 2) == 0) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+    
+    // helper method to find prime numbers using sieve of eratosthenes
+    public static boolean[] sieveOfEratosthenes(int n) {
+        boolean[] isPrime = new boolean[n+1];
+        Arrays.fill(isPrime, true);
+        isPrime[0] = false;
+        isPrime[1] = false;
+        
+        for (int i = 2; i * i <= n; i++) {
+            if (isPrime[i]) {
+                for (int j = i * i; j <= n; j += i) {
+                    isPrime[j] = false;
+                }
+            }
+        }
+        return isPrime;
+    }
+}
+
+// https://leetcode.com/problems/closest-prime-numbers-in-range/description/