Longest palindromic substring

leetcode/src/problems.rs

@@ -1,4 +1,5 @@
 pub mod add_two_numbers;
+pub mod longest_palindromic_substring;
 pub mod longest_substring;
 pub mod median_of_two_sorted_arrays;
 pub mod two_sum;

leetcode/src/problems/longest_palindromic_substring.rs

@@ -0,0 +1,24 @@
+use super::{Difficulty, Problem, Topic};
+
+pub struct LongestPalindromicSubstring;
+
+impl Problem for LongestPalindromicSubstring {
+    fn id(&self) -> usize {
+        5
+    }
+    fn difficulty(&self) -> Difficulty {
+        Difficulty::Medium
+    }
+    fn topic(&self) -> Topic {
+        Topic::Algorithms
+    }
+    fn title(&self) -> String {
+        "Longest Palindromic Substring".into()
+    }
+    fn description(&self) -> String {
+        r#"Given a string s, return the longest palindromic substring in s."#.into()
+    }
+    fn labels(&self) -> Vec<String> {
+        ["String".into(), "DP".into()].into()
+    }
+}

leetcode/src/solutions.rs

@@ -1,6 +1,7 @@
 use anyhow::Result;
 
 pub mod add_two_numbers;
+pub mod longest_palindromic_substring;
 pub mod longest_substring;
 pub mod median_of_two_sorted_arrays;
 pub mod two_sum;

leetcode/src/solutions/longest_palindromic_substring.rs

@@ -0,0 +1,73 @@
+use super::Solution;
+use std::collections::HashMap;
+
+pub struct LongestPalindromicSubstring;
+
+impl Solution for LongestPalindromicSubstring {
+    fn name(&self) -> String {
+        "Solution for Longest Palindromic Substring".into()
+    }
+    fn problem_id(&self) -> usize {
+        5
+    }
+    fn location(&self) -> String {
+        crate::location!()
+    }
+    fn test(&self) -> anyhow::Result<()> {
+        let testcases = [("babad", "bab"), ("cbbd", "bb")];
+
+        for (input, expect) in testcases {
+            let output = Self::longest_palindrome(input.into());
+
+            if expect != output {
+                anyhow::bail!("test failed for input={input}, expect={expect}, output={output}");
+            }
+        }
+
+        Ok(())
+    }
+    fn benchmark(&self) -> anyhow::Result<usize> {
+        todo!()
+    }
+}
+
+impl LongestPalindromicSubstring {
+    pub fn longest_palindrome(s: String) -> String {
+        let mut max = "";
+        let mut map: HashMap<char, Vec<_>> = HashMap::new();
+
+        for (end, ch) in s.chars().enumerate() {
+            map.entry(ch).or_default().push(end);
+
+            for &start in map.get(&ch).unwrap_or(&vec![]) {
+                let subs = &s[start..end + 1];
+
+                if Self::check_palindromic(subs) {
+                    if subs.len() > max.len() {
+                        max = subs;
+                    }
+                    break;
+                }
+            }
+        }
+
+        max.into()
+    }
+
+    fn check_palindromic(s: &str) -> bool {
+        let chars: Vec<_> = s.chars().collect();
+        let len = chars.len();
+        let mut p1 = 0;
+        let mut p2 = len - 1;
+
+        while p1 < p2 {
+            if chars[p1] != chars[p2] {
+                return false;
+            }
+            p1 += 1;
+            p2 -= 1;
+        }
+
+        true
+    }
+}

runtime/src/registration.rs

@@ -16,6 +16,12 @@ pub fn register_all(handle: ContainerHandle) -> anyhow::Result<()> {
     handle.register_problem(|_| problems::median_of_two_sorted_arrays::MedianOfTwoSortedArrays)?;
     handle
         .register_solution(|_| solutions::median_of_two_sorted_arrays::MedianOfTwoSortedArrays)?;
+    handle.register_problem(|_| {
+        problems::longest_palindromic_substring::LongestPalindromicSubstring
+    })?;
+    handle.register_solution(|_| {
+        solutions::longest_palindromic_substring::LongestPalindromicSubstring
+    })?;
 
     Ok(())
 }