feat: add rust solution to lcof problem: No.09 (doocs#669)

面试题 09. 用两个栈实现队列

Author: YangFong

lcof/面试题09. 用两个栈实现队列/README.md

@@ -244,6 +244,53 @@ class CQueue {
  */
 ```
 
+### **Rust**
+
+```rust
+struct CQueue {
+    s1: Vec<i32>,
+    s2: Vec<i32>
+}
+
+
+/**
+ * `&self` means the method takes an immutable reference.
+ * If you need a mutable reference, change it to `&mut self` instead.
+ */
+impl CQueue {
+
+    fn new() -> Self {
+        CQueue {
+            s1: Vec::new(),
+            s2: Vec::new(),
+        }
+    }
+    
+    fn append_tail(&mut self, value: i32) {
+        self.s1.push(value);
+    }
+    
+    fn delete_head(&mut self) -> i32 {
+        match self.s2.pop() {
+            Some(value) => value,
+            None => {
+                while !self.s1.is_empty() {
+                    self.s2.push(self.s1.pop().unwrap());
+                }
+                self.s2.pop().unwrap_or(-1)
+            }
+        }
+    }
+}
+
+/**
+ * Your CQueue object will be instantiated and called as such:
+ * let obj = CQueue::new();
+ * obj.append_tail(value);
+ * let ret_2: i32 = obj.delete_head();
+ */
+```
+
 ### **...**
 
 ```

lcof/面试题09. 用两个栈实现队列/Solution.rs

@@ -0,0 +1,42 @@
+struct CQueue {
+    s1: Vec<i32>,
+    s2: Vec<i32>
+}
+
+
+/**
+ * `&self` means the method takes an immutable reference.
+ * If you need a mutable reference, change it to `&mut self` instead.
+ */
+impl CQueue {
+
+    fn new() -> Self {
+        CQueue {
+            s1: Vec::new(),
+            s2: Vec::new(),
+        }
+    }
+    
+    fn append_tail(&mut self, value: i32) {
+        self.s1.push(value);
+    }
+    
+    fn delete_head(&mut self) -> i32 {
+        match self.s2.pop() {
+            Some(value) => value,
+            None => {
+                while !self.s1.is_empty() {
+                    self.s2.push(self.s1.pop().unwrap());
+                }
+                self.s2.pop().unwrap_or(-1)
+            }
+        }
+    }
+}
+
+/**
+ * Your CQueue object will be instantiated and called as such:
+ * let obj = CQueue::new();
+ * obj.append_tail(value);
+ * let ret_2: i32 = obj.delete_head();
+ */