Rust Solution added

Author: K11E3R

solution/1700-1799/1701.Average Waiting Time/README_EN.md

@@ -159,6 +159,24 @@ function averageWaitingTime(customers: number[][]): number {
 }
 ```
 
+#### Rust
+
+```rust
+impl Solution {
+    pub fn average_waiting_time(customers: Vec<Vec<i32>>) -> f64 {
+        let mut spent_time = 0;
+        let mut time_waited = 0;
+        for customer in &customers {
+            let a = customer[0] as i64;
+            let b = customer[1] as i64;
+            time_waited = time_waited.max(a) + b;
+            spent_time += time_waited - a;
+        }
+        spent_time as f64 / (customers.len() as f64)
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->