Define queue struct & add is_empty function

rust/src/queue.rs

@@ -0,0 +1,38 @@
+pub struct Queue<T> {
+    items: Vec<T>,
+    start: usize,
+    size: usize,
+    capacity: usize
+}
+
+impl<T> Queue<T> {
+    pub fn is_empty(&self) -> bool {
+        self.size == 0
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use once_cell::sync::Lazy;
+
+    static EMPTY_QUEUE: Queue<i8> = Queue {
+        items: Vec::new(),
+        start: 0,
+        size: 0,
+        capacity: 1
+    };
+
+    static INT_QUEUE: Lazy<Queue<i8>> = Lazy::new(|| Queue {
+        items: vec![1, 2, 3, 4],
+        start: 0,
+        size: 4,
+        capacity: 5
+    });
+
+    #[test]
+    fn test_is_empty() {
+        assert_eq!(EMPTY_QUEUE.is_empty(), true);
+        assert_eq!(INT_QUEUE.is_empty(), false);
+    }
+}