Longest Palindrome

easycodingAlgorithmsHash MapStringsGreedy~20 min

Asked at Google, Meta

Overview

Given a string s consisting of lowercase and/or uppercase letters, return the length of the longest palindrome that can be built with those letters. Letters are case-sensitive.

Constraints

1 <= s.length <= 2000
s consists of lowercase and uppercase English letters.

Examples

longestPalindrome("abccccdd");
// => 7  (e.g. "dccaccd")

longestPalindrome("a");
// => 1

Solution

Reveal solution

function longestPalindrome(s) {
  const freq = {};
  for (const c of s) freq[c] = (freq[c] || 0) + 1;
  let length = 0;
  let hasOdd = false;
  for (const count of Object.values(freq)) {
    length += Math.floor(count / 2) * 2;
    if (count % 2 === 1) hasOdd = true;
  }
  return hasOdd ? length + 1 : length;
}

Count character frequencies. Use pairs for both sides, and add one odd character in the center if any exist.

Resources

Longest Palindrome — LeetCode

longest-palindrome-build.js

Longest Palindrome

easycodingAlgorithmsHash Map

Overview

Given a string s consisting of lowercase and/or uppercase letters, return the length of the longest palindrome that can be built with those letters. Letters are case-sensitive.

Constraints

1 <= s.length <= 2000
s consists of lowercase and uppercase English letters.

Examples

longestPalindrome("abccccdd");
// => 7  (e.g. "dccaccd")

longestPalindrome("a");
// => 1

Solution

Reveal solution

function longestPalindrome(s) {
  const freq = {};
  for (const c of s) freq[c] = (freq[c] || 0) + 1;
  let length = 0;
  let hasOdd = false;
  for (const count of Object.values(freq)) {
    length += Math.floor(count / 2) * 2;
    if (count % 2 === 1) hasOdd = true;
  }
  return hasOdd ? length + 1 : length;
}

Count character frequencies. Use pairs for both sides, and add one odd character in the center if any exist.

Resources

Longest Palindrome — LeetCode

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