feat: add solution for design twitter in rust

Author: bujosa

src/medium/design_twitter.rs

@@ -0,0 +1,75 @@
+#![allow(dead_code)]
+use std::collections::BTreeMap;
+use std::collections::BTreeSet;
+use std::collections::VecDeque;
+
+#[derive(Default)]
+struct Twitter {
+    users: BTreeMap<i32, BTreeSet<i32>>,
+    tweets: VecDeque<(i32, i32)>,
+}
+
+impl Twitter {
+    fn new() -> Self {
+        Self::default()
+    }
+
+    fn post_tweet(&mut self, user_id: i32, tweet_id: i32) {
+        self.check_and_create_user_if_not_exist(user_id);
+        self.tweets.push_front((user_id, tweet_id));
+    }
+
+    fn get_news_feed(&mut self, user_id: i32) -> Vec<i32> {
+        self.check_and_create_user_if_not_exist(user_id);
+        let mut res = Vec::new();
+        let following = self.users.get(&user_id).unwrap();
+        for (usr_id, tweet_id) in &self.tweets {
+            if *usr_id == user_id || following.contains(&usr_id) {
+                res.push(*tweet_id);
+                if res.len() == 10 {
+                    break;
+                }
+            }
+        }
+        res
+    }
+
+    fn follow(&mut self, follower_id: i32, followee_id: i32) {
+        self.check_and_create_user_if_not_exist(follower_id);
+        self.users
+            .get_mut(&follower_id)
+            .unwrap()
+            .insert(followee_id);
+    }
+
+    fn unfollow(&mut self, follower_id: i32, followee_id: i32) {
+        self.check_and_create_user_if_not_exist(follower_id);
+        self.users
+            .get_mut(&follower_id)
+            .unwrap()
+            .remove(&followee_id);
+    }
+
+    fn check_and_create_user_if_not_exist(&mut self, follower_id: i32) {
+        if let None = self.users.get(&follower_id) {
+            self.users.insert(follower_id, BTreeSet::new());
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_twitter() {
+        let mut twitter = Twitter::new();
+        twitter.post_tweet(1, 5);
+        assert_eq!(twitter.get_news_feed(1), vec![5]);
+        twitter.follow(1, 2);
+        twitter.post_tweet(2, 6);
+        assert_eq!(twitter.get_news_feed(1), vec![6, 5]);
+        twitter.unfollow(1, 2);
+        assert_eq!(twitter.get_news_feed(1), vec![5]);
+    }
+}

src/readme.md

@@ -83,7 +83,7 @@
   - [x] [271. Encode and decode strings](../src/medium/encode_and_decode_strings.rs) -> [Problem Description](../src/medium/readme.md#271-encode-and-decode-strings)
   - [x] [287. Find the duplicate number](../src/medium/find_the_duplicate_number.rs) -> [Problem Description](../src/medium/readme.md#287-find-the-duplicate-number)
   - [x] [347. Top k frequent elements](../src/medium/top_k_frequent_elements.rs) -> [Problem Description](../src/medium/readme.md#347-top-k-frequent-elements)
-  - [ ] [355. Design twitter](../src/medium/design_twitter.rs) -> [Problem Description](../src/medium/readme.md#355-design-twitter)
+  - [x] [355. Design twitter](../src/medium/design_twitter.rs) -> [Problem Description](../src/medium/readme.md#355-design-twitter)
   - [x] [424. Longest repeating character replacement](../src/medium/longest_repeating_character_replacement.rs) -> [Problem Description](../src/medium/readme.md#424-longest-repeating-character-replacement)
   - [x] [567. Permutation in string](../src/medium/permutation_in_string.rs) -> [Problem Description](../src/medium/readme.md#567-permutation-in-string)
   - [x] [621. Task scheduler](../src/medium/task_scheduler.rs) -> [Problem Description](../src/medium/readme.md#621-task-scheduler)

theory/categories/6.heap_priority_queue/readme.md

@@ -68,11 +68,11 @@ A priority queue can be implemented using a heap.
 - [x] [K Closest Points to Origin](https://leetcode.com/problems/k-closest-points-to-origin/) | Medium | [Solution](../../../src/medium/k_closest_points_to_origin.rs) | [Problem Description](../../../src/medium/readme.md#973-k-closest-points-to-origin)
 - [x] [Kth Largest Element in an Array](https://leetcode.com/problems/kth-largest-element-in-an-array/) | Medium | [Solution](../../../src/medium/kth_largest_element_in_an_array.rs) | [Problem Description](../../../src/medium/readme.md#215-kth-largest-element-in-an-array)
 - [x] [Task Scheduler](https://leetcode.com/problems/task-scheduler/) | Medium | [Solution](../../../src/medium/task_scheduler.rs) | [Problem Description](../../../src/medium/readme.md#621-task-scheduler)
-- [ ] [Design Twitter](https://leetcode.com/problems/design-twitter/) | Medium | [Solution](../../../src/medium/design_twitter.rs) | [Problem Description](../../../src/medium/readme.md#355-design-twitter)
+- [x] [Design Twitter](https://leetcode.com/problems/design-twitter/) | Medium | [Solution](../../../src/medium/design_twitter.rs) | [Problem Description](../../../src/medium/readme.md#355-design-twitter)
 - [ ] [Find Median from Data Stream](https://leetcode.com/problems/find-median-from-data-stream/) | Hard | [Solution](../../../src/hard/find_median_from_data_stream.rs) | [Problem Description](../../../src/hard/readme.md#295-find-median-from-data-stream)
 
 Category: `Heap / Priority Queue`
 Created on: 2023-11-02 21:12
-Last modified on: 2023-11-03 22:13
+Last modified on: 2023-11-04 00:06
 Status: In Progress
 Author: [David Bujosa](https://github.com/bujosa)