feat: add rust solution to lc problem: No.2240 (#1562)

No.2240.Number of Ways to Buy Pens and Pencils

Author: poltao

solution/2200-2299/2240.Number of Ways to Buy Pens and Pencils/README.md

@@ -122,6 +122,20 @@ function waysToBuyPensPencils(total: number, cost1: number, cost2: number): numb
 }
 ```
 
+### **Rust**
+
+```rust
+impl Solution {
+    pub fn ways_to_buy_pens_pencils(total: i32, cost1: i32, cost2: i32) -> i64 {
+        let mut ans: i64 = 0;
+        for pen in 0..=total / cost1 {
+            ans += ((total - pen * cost1) / cost2) as i64 + 1;
+        }
+        ans
+    }
+}
+```
+
 ### **...**
 
 ```

solution/2200-2299/2240.Number of Ways to Buy Pens and Pencils/README_EN.md

@@ -108,6 +108,20 @@ function waysToBuyPensPencils(total: number, cost1: number, cost2: number): numb
 }
 ```
 
+### **Rust**
+
+```rust
+impl Solution {
+    pub fn ways_to_buy_pens_pencils(total: i32, cost1: i32, cost2: i32) -> i64 {
+        let mut ans: i64 = 0;
+        for pen in 0..=total / cost1 {
+            ans += ((total - pen * cost1) / cost2) as i64 + 1;
+        }
+        ans
+    }
+}
+```
+
 ### **...**
 
 ```

solution/2200-2299/2240.Number of Ways to Buy Pens and Pencils/Solution.rs

@@ -0,0 +1,9 @@
+impl Solution {
+    pub fn ways_to_buy_pens_pencils(total: i32, cost1: i32, cost2: i32) -> i64 {
+        let mut ans: i64 = 0;
+        for pen in 0..=total / cost1 {
+            ans += ((total - pen * cost1) / cost2) as i64 + 1;
+        }
+        ans
+    }
+}