Add problem 3381: Maximum Subarray Sum With Length Divisible by K

Author: EFanZh

src/lib.rs

@@ -2210,6 +2210,7 @@ pub mod problem_3371_identify_the_largest_outlier_in_an_array;
 pub mod problem_3375_minimum_operations_to_make_array_values_equal_to_k;
 pub mod problem_3376_minimum_time_to_break_locks_i;
 pub mod problem_3379_transformed_array;
+pub mod problem_3381_maximum_subarray_sum_with_length_divisible_by_k;
 
 #[cfg(test)]
 mod test_utilities;

src/problem_3381_maximum_subarray_sum_with_length_divisible_by_k/mod.rs

@@ -0,0 +1,22 @@
+pub mod modular_arithmetic;
+
+pub trait Solution {
+    fn max_subarray_sum(nums: Vec<i32>, k: i32) -> i64;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [
+            ((&[1, 2] as &[_], 1), 3),
+            ((&[-1, -2, -3, -4, -5], 4), -10),
+            ((&[-5, 1, 2, -3, 4], 2), 4),
+        ];
+
+        for ((nums, k), expected) in test_cases {
+            assert_eq!(S::max_subarray_sum(nums.to_vec(), k), expected);
+        }
+    }
+}

src/problem_3381_maximum_subarray_sum_with_length_divisible_by_k/modular_arithmetic.rs

@@ -0,0 +1,48 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl Solution {
+    pub fn max_subarray_sum(nums: Vec<i32>, k: i32) -> i64 {
+        let mut buckets = vec![i64::MAX / 2; k.cast_unsigned() as _].into_boxed_slice();
+        let mut bucket_index = 0;
+        let mut result = i64::MIN;
+        let mut sum = 0;
+
+        assert_ne!(buckets.len(), 0);
+
+        buckets[0] = 0;
+
+        for num in nums {
+            bucket_index += 1;
+
+            if bucket_index >= buckets.len() {
+                bucket_index = 0;
+            }
+
+            let bucket = &mut buckets[bucket_index];
+
+            sum += i64::from(num);
+            result = result.max(sum - *bucket);
+            *bucket = (*bucket).min(sum);
+        }
+
+        result
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn max_subarray_sum(nums: Vec<i32>, k: i32) -> i64 {
+        Self::max_subarray_sum(nums, k)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}