catch-up

implement-queue-using-stacks/sol.rs

@@ -0,0 +1,54 @@
+#[derive(Default)]
+struct MyQueue {
+    front: Vec<i32>,
+    back: Vec<i32>
+}
+
+// This solution has a maximum complexity of O(n) for
+// all the operations combined, but a single operation
+// could also be O(n) (apart from push and empty which
+// is always O(1))
+/** 
+ * `&self` means the method takes an immutable reference.
+ * If you need a mutable reference, change it to `&mut self` instead.
+ */
+impl MyQueue {
+
+    fn new() -> Self {
+        Default::default()
+    }
+
+    fn flush(&mut self) {
+        if self.front.is_empty() {
+            while let Some(n) = self.back.pop() { 
+                self.front.push(n);
+            }
+        }
+    }
+    
+    fn push(&mut self, x: i32) {
+        self.back.push(x)
+    }
+    
+    fn pop(&mut self) -> i32 {
+        self.flush();
+        self.front.pop().unwrap() // Unsafe unwrap because of instructions
+    }
+    
+    fn peek(&mut self) -> i32 {
+        self.flush();
+        *self.front.last().unwrap() // Unsafe unwrap because of instructions
+    }
+    
+    fn empty(&self) -> bool {
+        self.front.is_empty() && self.back.is_empty()
+    }
+}
+/**
+ * Your MyQueue object will be instantiated and called as such:
+ * let obj = MyQueue::new();
+ * obj.push(x);
+ * let ret_2: i32 = obj.pop();
+ * let ret_3: i32 = obj.peek();
+ * let ret_4: bool = obj.empty();
+ */