feat: add solution for problem 5 in rust

Author: bujosa

src/medium/longest_palindromic_substring.rs

@@ -0,0 +1,31 @@
+#![allow(dead_code)]
+pub fn longest_palindrome(s: String) -> String {
+    let chars: Vec<char> = s.chars().collect();
+    let mut res = String::new();
+
+    for i in 0..s.len() {
+        for &(l, r) in [(i, i), (i, i + 1)].iter() {
+            let (mut l, mut r) = (l, r);
+            while l <= r && r < s.len() && chars[l] == chars[r] {
+                if r - l + 1 > res.len() {
+                    res = s[l..=r].to_string();
+                }
+                if l == 0 {
+                    break;
+                }
+                l -= 1;
+                r += 1;
+            }
+        }
+    }
+
+    res
+}
+
+#[test]
+fn test_longest_palindrome() {
+    assert_eq!(longest_palindrome("babad".to_string()), "bab".to_string());
+    assert_eq!(longest_palindrome("cbbd".to_string()), "bb".to_string());
+    assert_eq!(longest_palindrome("a".to_string()), "a".to_string());
+    assert_eq!(longest_palindrome("ac".to_string()), "a".to_string());
+}