Do daily

Author: Zanger67

my-submissions/m1922 v1.py

@@ -0,0 +1,39 @@
+class Solution:
+    def countGoodNumbers(self, n: int) -> int:
+        mod_val = 10 ** 9 + 7
+        # evens
+        evens = 1
+        tot_cases = (n // 2) + (n % 2)
+        prev = []
+        if tot_cases > 0 :
+            evens = 5
+            x = 1
+            while 2 * x <= tot_cases :
+                prev.append((x, evens))
+                evens = (evens * evens) % mod_val
+                x *= 2
+            while prev :
+                i, pow5 = prev.pop()
+                if x + i <= tot_cases :
+                    x += i
+                    evens *= pow5
+        
+        # odds
+        odds = 1
+        tot_cases = (n // 2)
+        prev = []
+        if tot_cases > 0 :
+            odds = 4
+            x = 1
+            while 2 * x <= tot_cases :
+                prev.append((x, odds))
+                odds = (odds * odds) % mod_val
+                x *= 2
+            while prev :
+                i, pow4 = prev.pop()
+                if x + i <= tot_cases :
+                    x += i
+                    odds *= pow4
+
+
+        return (evens * odds) % (mod_val)

my-submissions/m1922 v2 cleaned.py

@@ -0,0 +1,23 @@
+class Solution:
+    def countGoodNumbers(self, n: int) -> int:
+        def _helper(tot_cases: int, poww: int, mod_val: int = 10 ** 9 + 7) :
+            if tot_cases == 0 :
+                return 1
+            output, x = poww, 1
+            prev = []
+            while 2 * x <= tot_cases :
+                prev.append((x, output))
+                output = (output * output) % mod_val
+                x *= 2
+            while prev :
+                i, poww = prev.pop()
+                if x + i <= tot_cases :
+                    x += i
+                    output = (output * poww) % mod_val
+            return output
+
+        mod_val = 10 ** 9 + 7
+        return (
+            _helper((n // 2) + (n % 2), 5, mod_val) * 
+            _helper((n // 2), 4, mod_val)
+        ) % (mod_val)