README.md

516. Longest Palindromic Subsequence

Given a string s, find the longest palindromic subsequence's length in s.

A subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements.

Example 1:

Input: s = "bbbab"
Output: 4
Explanation: One possible longest palindromic subsequence is "bbbb".

Example 2:

Input: s = "cbbd"
Output: 2
Explanation: One possible longest palindromic subsequence is "bb".

Constraints:

• 1 <= s.length <= 1000
• s consists only of lowercase English letters.

Solutions (Rust)

1. Solution

impl Solution {
    pub fn longest_palindrome_subseq(s: String) -> i32 {
        let s = s.as_bytes();
        let mut dp = vec![vec![0; s.len()]; s.len()];

        for i in 0..s.len() {
            dp[i][i] = 1;
        }

        for size in 2..=s.len() {
            for i in 0..s.len() - size + 1 {
                dp[i][i + size - 1] =
                    dp[i + 1][i + size - 2] + (s[i] == s[i + size - 1]) as i32 * 2;
                dp[i][i + size - 1] = dp[i][i + size - 1]
                    .max(dp[i][i + size - 2])
                    .max(dp[i + 1][i + size - 1]);
            }
        }

        dp[0][s.len() - 1]
    }
}