Update algorithm8.rs

Author: hellolutar

exercises/algorithm/algorithm8.rs

@@ -2,7 +2,6 @@
 	queue
 	This question requires you to use queues to implement the functionality of the stac
 */
-// I AM NOT DONE
 
 #[derive(Debug)]
 pub struct Queue<T> {
@@ -67,15 +66,24 @@ impl<T> myStack<T> {
         }
     }
     pub fn push(&mut self, elem: T) {
-        //TODO
+        self.q1.enqueue(elem);
     }
     pub fn pop(&mut self) -> Result<T, &str> {
-        //TODO
-		Err("Stack is empty")
+        if self.q1.size() == 0 {
+            return Err("Stack is empty");
+        }
+        while self.q1.size() > 1 {
+            self.q2.enqueue(self.q1.dequeue().unwrap());
+        }
+
+        let top = self.q1.dequeue().unwrap();
+
+        std::mem::swap(&mut self.q1, &mut self.q2);
+
+        Ok(top)
     }
     pub fn is_empty(&self) -> bool {
-		//TODO
-        true
+        self.q1.is_empty()
     }
 }
 
@@ -101,4 +109,4 @@ mod tests {
         assert_eq!(s.pop(), Err("Stack is empty"));
         assert_eq!(s.is_empty(), true);
 	}
-}
+}