Good afternoon! Here's our prompt for today.

Question/Prompt

A palindrome is a word, phrase, or sequence that reads the same backward or forwards. A palindromic subsequence is a palindrome derived from a sequence by deleting some or no elements from it. This subsequence is formed without changing the order of the elements in the original sequence.

Given a string s, can you find the length of the longest palindromic subsequence of s?

For example, if s = "bbbab", then the longest palindromic subsequence is bbbb. The length of this subsequence is 4, which is the required answer.

Constraints

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

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

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var assert = require('assert');

​

function longestPalindromeSubseq(s) {

    // add your code here

    return;

}

​

try {

    assert.deepEqual(longestPalindromeSubseq('bbbab'), 4);

    console.log('PASSED: ' + "`longestPalindromeSubseq('bbbab')` should return `4`");

} catch (err) {

    console.log(err);

}

​

try {

    assert.deepEqual(longestPalindromeSubseq('cbbd'), 2);

    console.log('PASSED: ' + "`longestPalindromeSubseq('cbbd')` should return `2`");

} catch (err) {

    console.log(err);

}

​

try {

    assert.deepEqual(longestPalindromeSubseq('abbcdabbc'), 5);

    console.log('PASSED: ' + "`longestPalindromeSubseq('abbcdabbc')` should return `5`");

} catch (err) {

    console.log(err);

}

​

Here's our guided, illustrated walk-through.

How do I use this guide?