feat: add rust solution to lc problem: No.2485 (doocs#1306)

Signed-off-by: xiaolatiao <1628652790@qq.com>

Author: dierbei

solution/2400-2499/2485.Find the Pivot Integer/README.md

@@ -223,6 +223,23 @@ class Solution {
 }
 ```
 
+### **Rust**
+
+```rust
+impl Solution {
+    pub fn pivot_integer(n: i32) -> i32 {
+        let y = n * (n + 1) / 2;
+        let x = (y as f64).sqrt() as i32;
+
+        if x * x == y {
+            return x;
+        }
+
+        -1
+    }
+}
+```
+
 ### **...**
 
 ```

solution/2400-2499/2485.Find the Pivot Integer/README_EN.md

@@ -186,6 +186,23 @@ class Solution {
 }
 ```
 
+### **Rust**
+
+```rust
+impl Solution {
+    pub fn pivot_integer(n: i32) -> i32 {
+        let y = n * (n + 1) / 2;
+        let x = (y as f64).sqrt() as i32;
+
+        if x * x == y {
+            return x;
+        }
+
+        -1
+    }
+}
+```
+
 ### **...**
 
 ```

solution/2400-2499/2485.Find the Pivot Integer/Solution.rs

@@ -0,0 +1,12 @@
+impl Solution {
+    pub fn pivot_integer(n: i32) -> i32 {
+        let y = n * (n + 1) / 2;
+        let x = (y as f64).sqrt() as i32;
+
+        if x * x == y {
+            return x;
+        }
+
+        -1
+    }
+}