Create 1922_Count_Good_Numbers.java

Author: vishwajeetmishra4

JAVA/1922_Count_Good_Numbers.java

@@ -0,0 +1,19 @@
+// Problem Number: 1922
+
+// Count Good Numbers.
+
+class Solution {
+  public int countGoodNumbers(long n) {
+    return (int) (modPow(4 * 5, n / 2) * (n % 2 == 0 ? 1 : 5) % MOD);
+  }
+
+  private static final int MOD = 1_000_000_007;
+
+  private long modPow(long x, long n) {
+    if (n == 0)
+      return 1;
+    if (n % 2 == 1)
+      return x * modPow(x, n - 1) % MOD;
+    return modPow(x * x % MOD, n / 2);
+  }
+}