Solve reverse-integer.

source/lib.rs

@@ -1 +1,2 @@
+pub mod reverse_integer;
 pub mod two_sum;

source/reverse_integer/mod.rs

@@ -0,0 +1,26 @@
+pub fn reverse(number: i32) -> i32 {
+  number
+    // Convert to an absolute number without wrapping or panicking.
+    .unsigned_abs()
+    // Convert the number to string, then reverse all its characters.
+    .to_string()
+    .chars()
+    .rev()
+    // Collect the reversed characters back into a string.
+    .collect::<String>()
+    // Parse the string into an i32.
+    .parse()
+    // If it returns an Err then use 0 instead.
+    .unwrap_or(0)
+    // Then multiply by 0, 1 or -1 depending on the sign of the original number.
+    * number.signum()
+}
+
+#[test]
+fn test_reverse_integer() {
+  assert_eq!(reverse(123), 321);
+  assert_eq!(reverse(-123), -321);
+  assert_eq!(reverse(120), 21);
+  assert_eq!(reverse(i32::MAX), 0);
+  assert_eq!(reverse(i32::MIN), 0);
+}