Solve palindrome-number.

source/lib.rs

@@ -1,2 +1,3 @@
+pub mod palindrome_number;
 pub mod reverse_integer;
 pub mod two_sum;

source/palindrome_number/mod.rs

@@ -0,0 +1,23 @@
+pub fn is_palindrome(number: i32) -> bool {
+  // Negative numbers can never be a palindrome because of the minus sign.
+  if number < 0 {
+    return false;
+  }
+
+  let number_string = number.to_string();
+  number_string == number_string.chars().rev().collect::<String>()
+}
+
+#[test]
+fn test_palindrome_number() {
+  assert!(is_palindrome(0));
+  assert!(is_palindrome(-0));
+  assert!(is_palindrome(1));
+  assert!(is_palindrome(121));
+  assert!(is_palindrome(12321));
+
+  assert!(!is_palindrome(123));
+  assert!(!is_palindrome(321));
+  assert!(!is_palindrome(10));
+  assert!(!is_palindrome(-121));
+}