20250413 finished.

src/problem/mod.rs

@@ -595,3 +595,5 @@ mod p3375_minimum_operations_to_make_array_values_equal_to_k;
 mod p2843_count_symmetric_integers;
 
 mod p3272_find_the_count_of_good_integers;
+
+mod p1922_count_good_numbers;

src/problem/p1922_count_good_numbers.rs

@@ -0,0 +1,49 @@
+/**
+ * [1922] Count Good Numbers
+ */
+pub struct Solution {}
+
+// submission codes start here
+
+const MOD: i64 = 1_000_000_000 + 7;
+
+impl Solution {
+    pub fn count_good_numbers(n: i64) -> i32 {
+        let mut result = Self::quick_power(20, n / 2);
+
+        if n % 2 == 1 {
+            result = result * 5 % MOD;
+        }
+
+        result as i32
+    }
+
+    fn quick_power(mut m: i64, mut n: i64) -> i64 {
+        let mut result = 1;
+
+        while n > 0 {
+            if n & 1 == 1 {
+                result = result * m % MOD;
+            }
+
+            m = m * m % MOD;
+            n = n >> 1;
+        }
+
+        result
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_1922() {
+        assert_eq!(5, Solution::count_good_numbers(1));
+        assert_eq!(400, Solution::count_good_numbers(4));
+        assert_eq!(564_908_303, Solution::count_good_numbers(50));
+    }
+}