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Commit c4f6c29

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516. Longest Palindromic Subsequence
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import 'dart:math';
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/// The time complexity of the `longestPalindromeSubseq` function is `O(n^2)`,
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/// where `n` is the length of the input string `s`. This is because the function
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/// uses a dynamic programming approach to compute the length of the longest
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/// palindromic subsequence of `s`, which involves filling in an `n * n` table of values.
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/// The space complexity of the function is also `O(n^2)`, since it uses a 2D list `dp`
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/// of size `n * n` to store the intermediate results of the dynamic programming algorithm.
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class Solution {
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int longestPalindromeSubseq(String s) {
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int n = s.length;
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List<List<int>> dp = List.generate(n, (_) => List.filled(n, 0));
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for (int i = n - 1; i >= 0; i--) {
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dp[i][i] = 1;
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for (int j = i + 1; j < n; j++) {
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if (s[i] == s[j]) {
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dp[i][j] = dp[i + 1][j - 1] + 2;
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} else {
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dp[i][j] = max(dp[i + 1][j], dp[i][j - 1]);
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}
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}
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}
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return dp[0][n - 1];
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}
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}
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void main(List<String> args) {
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print(Solution().longestPalindromeSubseq('bbbab'));
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}
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/// NB: The time complexity of the `longestPalindromeSubseq` function
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/// is optimal at `O(n^2)`, where `n` is the length of the input string `s`.
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/// This is because any algorithm that solves the longest palindromic
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/// subsequence problem must examine every possible substring of `s`,
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/// which takes `O(n^2)` time.
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516. Longest Palindromic Subsequence
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https://leetcode.com/problems/longest-palindromic-subsequence/
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Given a string s, find the longest palindromic subsequence's length in s.
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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.
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Example 1:
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Input: s = "bbbab"
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Output: 4
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Explanation: One possible longest palindromic subsequence is "bbbb".
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Example 2:
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Input: s = "cbbd"
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Output: 2
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Explanation: One possible longest palindromic subsequence is "bb".
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Constraints:
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1 <= s.length <= 1000
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s consists only of lowercase English letters.

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