2025: day02: part 2

aoc2025/src/day02.rs

@@ -50,31 +50,15 @@ fn get_num_digits(num: &u64) -> usize {
     digits
 }
 
-fn get_nth_digit(num: &u64, n: usize) -> u64 {
-    let mut num = *num;
-    for _ in 0..n {
-        num /= 10;
-    }
-    num % 10
-}
-
 fn is_repeated_twice(num: &u64) -> bool {
     let num_digits = get_num_digits(num);
     if !num_digits.is_multiple_of(2) {
         return false;
     }
     let half = num_digits / 2;
+    let mask = 10_u64.pow(half as u32);
 
-    for (right, left) in (0..half).zip(half..num_digits) {
-        let ln = get_nth_digit(num, left);
-        let rn = get_nth_digit(num, right);
-
-        if ln != rn {
-            return false;
-        }
-    }
-
-    true
+    *num / mask == *num % mask
 }
 
 fn part1(input: &str) -> Result<u64> {