rs: add “Insert Delete GetRandom O(1)”

Signed-off-by: Matej Focko <mfocko@redhat.com>

rs/insert-delete-getrandom-o1.rs

@@ -0,0 +1,39 @@
+use rand::prelude::IteratorRandom;
+use std::collections::HashSet;
+
+struct RandomizedSet {
+    nums: HashSet<i32>,
+}
+
+impl RandomizedSet {
+    fn new() -> Self {
+        Self {
+            nums: HashSet::new(),
+        }
+    }
+
+    fn insert(&mut self, val: i32) -> bool {
+        self.nums.insert(val)
+    }
+
+    fn remove(&mut self, val: i32) -> bool {
+        self.nums.remove(&val)
+    }
+
+    fn get_random(&self) -> i32 {
+        let mut rng = rand::thread_rng();
+        *self
+            .nums
+            .iter()
+            .choose(&mut rng)
+            .expect("at least one number is in the set")
+    }
+}
+
+/*
+ * Your RandomizedSet object will be instantiated and called as such:
+ * let obj = RandomizedSet::new();
+ * let ret_1: bool = obj.insert(val);
+ * let ret_2: bool = obj.remove(val);
+ * let ret_3: i32 = obj.get_random();
+ */