feat: add rust solution to lc problem: No.2544 (#1234)

Author: dierbei

solution/2500-2599/2544.Alternating Digit Sum/README.md

@@ -166,6 +166,23 @@ impl Solution {
 }
 ```
 
+```rust
+impl Solution {
+    pub fn alternate_digit_sum(n: i32) -> i32 {
+        let mut ans = 0;
+        let mut sign = 1;
+
+        for c in format!("{}", n).chars() {
+            let x = c.to_digit(10).unwrap()as i32;
+            ans += x * sign;
+            sign *= -1;
+        }
+
+        ans
+    }
+}
+```
+
 ### **C**
 
 ```c

solution/2500-2599/2544.Alternating Digit Sum/README_EN.md

@@ -156,6 +156,23 @@ impl Solution {
 }
 ```
 
+```rust
+impl Solution {
+    pub fn alternate_digit_sum(n: i32) -> i32 {
+        let mut ans = 0;
+        let mut sign = 1;
+
+        for c in format!("{}", n).chars() {
+            let x = c.to_digit(10).unwrap()as i32;
+            ans += x * sign;
+            sign *= -1;
+        }
+
+        ans
+    }
+}
+```
+
 ### **C**
 
 ```c