From 741ea79b41cad3dae0cc0a81f2d901a37a02f906 Mon Sep 17 00:00:00 2001
From: EFanZh <efanzh@gmail.com>
Date: Tue, 21 Jan 2025 23:30:00 +0800
Subject: [PATCH] Add problem 2404: Most Frequent Even Element

---
 src/lib.rs                                    |  1 +
 .../hash_map.rs                               | 61 +++++++++++++++++++
 .../mod.rs                                    | 26 ++++++++
 3 files changed, 88 insertions(+)
 create mode 100644 src/problem_2404_most_frequent_even_element/hash_map.rs
 create mode 100644 src/problem_2404_most_frequent_even_element/mod.rs

diff --git a/src/lib.rs b/src/lib.rs
index ce23b6b8..b6adaa9a 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1790,6 +1790,7 @@ pub mod problem_2399_check_distances_between_same_letters;
 pub mod problem_2400_number_of_ways_to_reach_a_position_after_exactly_k_steps;
 pub mod problem_2401_longest_nice_subarray;
 pub mod problem_2402_meeting_rooms_iii;
+pub mod problem_2404_most_frequent_even_element;
 
 #[cfg(test)]
 mod test_utilities;
diff --git a/src/problem_2404_most_frequent_even_element/hash_map.rs b/src/problem_2404_most_frequent_even_element/hash_map.rs
new file mode 100644
index 00000000..e1a42506
--- /dev/null
+++ b/src/problem_2404_most_frequent_even_element/hash_map.rs
@@ -0,0 +1,61 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+use std::cmp::Ordering;
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+use std::hash::{BuildHasherDefault, DefaultHasher};
+
+impl Solution {
+    pub fn most_frequent_even(nums: Vec<i32>) -> i32 {
+        let mut frequencies = HashMap::<_, u16, _>::with_hasher(BuildHasherDefault::<DefaultHasher>::default());
+
+        for num in nums {
+            if num & 1 == 0 {
+                match frequencies.entry(num) {
+                    Entry::Occupied(occupied_entry) => *occupied_entry.into_mut() += 1,
+                    Entry::Vacant(vacant_entry) => {
+                        vacant_entry.insert(1);
+                    }
+                }
+            }
+        }
+
+        let mut result = -1;
+        let mut max_frequency = 0;
+
+        for (&num, &frequency) in &frequencies {
+            match frequency.cmp(&max_frequency) {
+                Ordering::Less => {}
+                Ordering::Equal => {
+                    if num < result {
+                        result = num;
+                    }
+                }
+                Ordering::Greater => {
+                    max_frequency = frequency;
+                    result = num;
+                }
+            }
+        }
+
+        result
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn most_frequent_even(nums: Vec<i32>) -> i32 {
+        Self::most_frequent_even(nums)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}
diff --git a/src/problem_2404_most_frequent_even_element/mod.rs b/src/problem_2404_most_frequent_even_element/mod.rs
new file mode 100644
index 00000000..1d985a4b
--- /dev/null
+++ b/src/problem_2404_most_frequent_even_element/mod.rs
@@ -0,0 +1,26 @@
+pub mod hash_map;
+
+pub trait Solution {
+    fn most_frequent_even(nums: Vec<i32>) -> i32;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [
+            (&[0, 1, 2, 2, 4, 4, 1] as &[_], 2),
+            (&[4, 4, 4, 9, 2, 4], 4),
+            (&[29, 47, 21, 41, 13, 37, 25, 7], -1),
+            (
+                &[8154, 9139, 8194, 3346, 5450, 9190, 133, 8239, 4606, 8671, 8412, 6290],
+                3346,
+            ),
+        ];
+
+        for (nums, expected) in test_cases {
+            assert_eq!(S::most_frequent_even(nums.to_vec()), expected);
+        }
+    }
+}