https://leetcode.com/problems/longest-palindrome/

longestPalindrome.js

/**
 * @param {string} s
 * @return {number}
 */
var longestPalindrome = function(s) {
    
    const counts = new Array(123 - 65).fill(0);
    const A = 'A'.charCodeAt(0);
    
    for(let i=0; i<s.length; i++){ // the only branching condition!
        counts[s.charCodeAt(i) - A]++;
    }
    
    let result = 0;
    let oddFound = 0;
    for(let i=0; i<counts.length; i++){ // assuming a compiler would unroll this ;)
        result   += (counts[i] - (counts[i]%2));
        oddFound |= (counts[i] & 1);
    }
    
    return result + oddFound;
};