Create 3272_Find_the_Count_of_Good_Integers.java

Author: vishwajeetmishra4

JAVA/3272_Find_the_Count_of_Good_Integers.java

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+// Problem Number: 3272
+
+// Find the Count of Good Integers.
+
+class Solution {
+  public long countGoodIntegers(int n, int k) {
+    final int halfLength = (n + 1) / 2;
+    final int minHalf = (int) Math.pow(10, halfLength - 1);
+    final int maxHalf = (int) Math.pow(10, halfLength);
+    long ans = 0;
+    Set<String> seen = new HashSet<>();
+
+    for (int num = minHalf; num < maxHalf; ++num) {
+      final String firstHalf = String.valueOf(num);
+      final String secondHalf = new StringBuilder(firstHalf).reverse().toString();
+      final String palindrome = firstHalf + secondHalf.substring(n % 2);
+      if (Long.parseLong(palindrome) % k != 0)
+        continue;
+      char[] sortedDigits = palindrome.toCharArray();
+      Arrays.sort(sortedDigits);
+      String sortedDigitsStr = new String(sortedDigits);
+      if (seen.contains(sortedDigitsStr))
+        continue;
+      seen.add(sortedDigitsStr);
+      int[] digitCount = new int[10];
+      for (char c : palindrome.toCharArray())
+        ++digitCount[c - '0'];
+
+      final int firstDigitChoices = n - digitCount[0];
+      long permutations = firstDigitChoices * factorial(n - 1);
+      
+      for (final int freq : digitCount)
+        if (freq > 1)
+          permutations /= factorial(freq);
+      ans += permutations;
+    }
+
+    return ans;
+  }
+
+  private long factorial(int n) {
+    long res = 1;
+    for (int i = 2; i <= n; ++i)
+      res *= i;
+    return res;
+  }
+}