Added Insert Delete GetRandom O(1)

Author: ryanoneill

Cargo.toml

@@ -6,3 +6,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+rand = "0.7.2"

src/insert_delete_getrandom_o1.rs

@@ -0,0 +1,112 @@
+use rand::prelude::*;
+use std::collections::HashMap;
+
+/// Implement the `RandomizedSet` class:
+///
+/// * `RandomizedSet()` Initializes the `RandomizedSet` object.
+///
+/// * `bool insert(int val)` Inserts an item `val` into the set if not present.
+///   Returns `true` if the item was not present, `false` otherwise.
+///
+/// * `bool remove(int val)` Removes an item `val` from the set if present.
+///   Returns `true` if the item was present, `false` otherwise.
+///
+/// * `int getRandom()` Returns a random element from the current set of
+///   elements (it's guaranteed that at least one element exists when the
+///   method is called). Each element must have the same probability of being
+///   returned.
+///
+/// You must implement the functions of the class such that each function works
+/// in average `O(1)` time complexity.
+struct RandomizedSet {
+    items: Vec<i32>,
+    indices: HashMap<i32, usize>
+}
+
+impl RandomizedSet {
+
+    fn new() -> Self {
+        Self { items: Vec::new(), indices: HashMap::new() }
+    }
+
+    fn insert(&mut self, val: i32) -> bool {
+        if !self.indices.contains_key(&val) {
+            let index = self.items.len();
+            self.items.push(val);
+            self.indices.insert(val, index);
+            true
+        } else { false }
+    }
+
+    fn remove(&mut self, val: i32) -> bool {
+        if self.indices.contains_key(&val) {
+            let n = self.items.len();
+            if n == 1 {
+                self.indices.clear();
+                self.items.clear();
+            } else {
+                let index = self.indices[&val];
+                if index == n-1 {
+                    self.items.pop();
+                    self.indices.remove(&val);
+                } else {
+                    self.items.swap_remove(index);
+                    self.indices.remove(&val);
+                    let value_at_index = self.items[index];
+                    self.indices.insert(value_at_index, index);
+                }
+            }
+            true
+        } else { false }
+    }
+
+    fn get_random(&self) -> i32 {
+        let n = self.items.len();
+        let mut rng = rand::thread_rng();
+        let index = rng.gen_range(0,n);
+        self.items[index]
+    }
+
+}
+
+#[cfg(test)]
+mod tests {
+    use super::RandomizedSet;
+
+    #[test]
+    fn example_1() {
+        let mut set = RandomizedSet::new();
+        let result = set.insert(1);
+        assert!(result);
+        let result = set.remove(2);
+        assert!(!result);
+        let result = set.insert(2);
+        assert!(result);
+        let result = set.get_random();
+        assert!(result == 1 || result == 2);
+        let result = set.remove(1);
+        assert!(result);
+        let result = set.insert(2);
+        assert!(!result);
+        let result = set.get_random();
+        assert_eq!(result, 2);
+    }
+
+    #[test]
+    fn real_world_1() {
+        let mut set = RandomizedSet::new();
+        let result = set.remove(0);
+        assert!(!result);
+        let result = set.remove(0);
+        assert!(!result);
+        let result = set.insert(0);
+        assert!(result);
+        let result = set.get_random();
+        assert_eq!(result, 0);
+        let result = set.remove(0);
+        assert!(result);
+        let result = set.insert(0);
+        assert!(result);
+    }
+
+}

src/lib.rs

@@ -149,6 +149,8 @@ pub mod intersection_of_two_arrays_ii; // 350
 
 pub mod kth_smallest_element_in_a_sorted_matrix; // 378
 
+pub mod insert_delete_getrandom_o1; // 380 ✓
+
 pub mod ransom_note; // 383
 
 pub mod first_unique_character_in_a_string;