Merge pull request #66 from InflixOP/patch1

Create #1922. Count Good Numbers.cpp

Author: InflixOP

#1922. Count Good Numbers.cpp

@@ -0,0 +1,18 @@
+class Solution {
+public:
+    int MOD = 1e9 + 7;
+    int countGoodNumbers(long long n) {
+        return (power(5, (n + 1) / 2) % MOD * power(4, n / 2) % MOD) % MOD;
+    }
+
+    long long power(long long x, long long n) {
+        if (n == 0)
+            return 1;
+        long long y = power(x, n / 2);
+        if (n % 2 == 0) {
+            return (y * y) % MOD;
+        } else {
+            return (x * y * y) % MOD;
+        }
+    }
+};