Add problem 3026: Maximum Good Subarray Sum

Author: EFanZh

src/lib.rs

@@ -2052,6 +2052,7 @@ pub mod problem_3016_minimum_number_of_pushes_to_type_word_ii;
 pub mod problem_3019_number_of_changing_keys;
 pub mod problem_3021_alice_and_bob_playing_flower_game;
 pub mod problem_3024_type_of_triangle;
+pub mod problem_3026_maximum_good_subarray_sum;
 
 #[cfg(test)]
 mod test_utilities;

src/problem_3026_maximum_good_subarray_sum/mod.rs

@@ -0,0 +1,22 @@
+pub mod prefix_sums;
+
+pub trait Solution {
+    fn maximum_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, 3, 4, 5, 6] as &[_], 1), 11),
+            ((&[-1, 3, 2, 4, 5], 3), 11),
+            ((&[-1, -2, -3, -4], 2), -6),
+        ];
+
+        for ((nums, k), expected) in test_cases {
+            assert_eq!(S::maximum_subarray_sum(nums.to_vec(), k), expected);
+        }
+    }
+}

src/problem_3026_maximum_good_subarray_sum/prefix_sums.rs

@@ -0,0 +1,53 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+use std::collections::HashMap;
+use std::collections::hash_map::Entry;
+
+impl Solution {
+    pub fn maximum_subarray_sum(nums: Vec<i32>, k: i32) -> i64 {
+        let mut num_to_prefix_sums = HashMap::<i32, i64>::new();
+        let mut prefix_sum = 0;
+        let mut result = i64::MIN;
+
+        for num in nums {
+            match num_to_prefix_sums.entry(num) {
+                Entry::Occupied(occupied_entry) => {
+                    let sum = occupied_entry.into_mut();
+
+                    *sum = (*sum).min(prefix_sum);
+                }
+                Entry::Vacant(vacant_entry) => {
+                    vacant_entry.insert(prefix_sum);
+                }
+            }
+
+            prefix_sum += i64::from(num);
+
+            for key in [num - k, num + k] {
+                if let Some(&sum) = num_to_prefix_sums.get(&key) {
+                    result = result.max(prefix_sum - sum);
+                }
+            }
+        }
+
+        if result == i64::MIN { 0 } else { result }
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn maximum_subarray_sum(nums: Vec<i32>, k: i32) -> i64 {
+        Self::maximum_subarray_sum(nums, k)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}