longest-palindrome.org

var longestPalindrome = function(s) {
  let ltrCount = Object.values( s.split("").reduce((struct, val) => {
    struct[val] = (struct[val] || 0) + 1;
    return struct;
  }, {}) );

  let pairs = ltrCount.map(n=>Math.floor(n/2)).reduce((acc,val)=>val+acc);

  if (pairs == s.length/2) {
    return s.length;
  } else {
    return pairs*2 + 1;
  }
};

given any number of letters return the longest palindrome you can make by rearranging letters

“bbasadeff”

facts about palindromes:

every letter appears with another of that letter, except for at most 1 letter(if it is center of odd-lengthed palindrome)

for every even numbered palindrome you can make it one longer by adding another letter in the middle

strategy

group letters into pairs

if there are any left over then the answer is 2(numOfPairs)+1

if there are none left over then the answer is the length of the input

Code strategy

filter out non pairs

using set to only show unique values

split to array

convert to Set

compare lengths

the difference is the number of pairs

if difference is exactly half return original length

if difference is not exactly half, then double difference and add 1

doesn’t account for letters that are repeated multiple times

using charcode to put in order

create a map of char counts

optimizations

remove unnecessary variables