Solution #2523 - Mridul/Edited - 07/06/2025

Daily Questions/2523 - Closest Prime Numbers in Range - Medium/Explanation.md

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+private static boolean[] isPrime = new boolean[1000001]; This boolean array is used to mark prime numbers up to 1000000. The size of the array is 1000001 to include the number 1000000.
+
+Static Block:
+The static block is used to initialize the isPrime array and precompute the prime numbers.
+
+Arrays.fill(isPrime, true); This method sets all elements of the isPrime array to true, assuming all numbers are prime initially.
+
+precompute(); This method is called to mark non-prime numbers in the isPrime array.
+
+Method: precompute()
+This method uses the Sieve of Eratosthenes algorithm to mark non-prime numbers in the isPrime array.
+
+isPrime[0] = isPrime[1] = false; Numbers 0 and 1 are not prime.
+
+A loop is used to iterate from 2 to sqrt(1000000).
+
+If isPrime[i] is true, all multiples of i are marked as false (not prime) starting from i*i.
+
+Method: closestPrimes(int left, int right)
+This method finds the closest prime numbers within the range [left, right].
+
+int prev = -1, minDiff = Integer.MAX_VALUE; Variables to track the previous prime number and the minimum difference between consecutive primes.
+
+int num1 = -1, num2 = -1; Variables to store the closest prime numbers.
+
+A loop iterates through the range [left, right].
+
+If isPrime[i] is true, the number i is a prime.
+
+If prev is not -1 and the difference (i - prev) is less than minDiff, update minDiff and set num1 to prev and num2 to i.
+
+Update prev to i.
+
+If no prime numbers are found, return new int[]{-1, -1}. Otherwise, return the closest prime numbers num1 and num2.

Daily Questions/2523 - Closest Prime Numbers in Range - Medium/Solution.java

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+import java.util.*;
+
+class Solution {
+    private static boolean[] isPrime = new boolean[1000001];
+
+    static {
+        Arrays.fill(isPrime, true);
+        precompute();
+    }
+
+    private static void precompute() {
+        isPrime[0] = isPrime[1] = false;
+        for (int i = 2; i * i <= 1000000; i++) {
+            if (isPrime[i]) {
+                for (int j = i * i; j <= 1000000; j += i) {
+                    isPrime[j] = false;
+                }
+            }
+        }
+    }
+
+    public int[] closestPrimes(int left, int right) {
+        int prev = -1, minDiff = Integer.MAX_VALUE;
+        int num1 = -1, num2 = -1;
+
+        for (int i = left; i <= right; i++) {
+            if (isPrime[i]) {
+                if (prev != -1 && (i - prev < minDiff)) {
+                    minDiff = i - prev;
+                    num1 = prev;
+                    num2 = i;
+                }
+                prev = i;
+            }
+        }
+
+        return (num1 == -1) ? new int[]{-1, -1} : new int[]{num1, num2};
+    }
+}