3517. Smallest Palindromic Rearrangement I

class Solution {
    public String smallestPalindrome(String s) {
        int[] freq = new int[26];
        for (char c : s.toCharArray()) {
            freq[c - 'a']++;
        }
        StringBuilder left = new StringBuilder();
        String middle = "";
        for (int i = 0; i < 26; i++) {
            while (freq[i] >= 2) {
                left.append((char) ('a' + i));
                freq[i] -= 2;
            }
            if (freq[i] == 1) {
                middle = String.valueOf((char) ('a' + i));
            }
        }
        StringBuilder right = new StringBuilder(left).reverse();
        return left.toString() + middle + right.toString();
    }
}

class Solution:
    def smallestPalindrome(self, s):
        freq = [0] * 26

        for c in s:
            freq[ord(c) - ord('a')] += 1

        left = []
        middle = ""

        for i in range(26):
            while freq[i] >= 2:
                left.append(chr(ord('a') + i))
                freq[i] -= 2

            if freq[i] == 1:
                middle = chr(ord('a') + i)

        return "".join(left) + middle + "".join(reversed(left))

class Solution {
public:
    string smallestPalindrome(string s) {
        vector<int> freq(26, 0);

        for (char c : s) {
            freq[c - 'a']++;
        }

        string left = "";
        string middle = "";

        for (int i = 0; i < 26; i++) {
            while (freq[i] >= 2) {
                left += char('a' + i);
                freq[i] -= 2;
            }

            if (freq[i] == 1) {
                middle = char('a' + i);
            }
        }

        string right = left;
        reverse(right.begin(), right.end());

        return left + middle + right;
    }
};

var smallestPalindrome = function(s) {
    const freq = new Array(26).fill(0);

    for (const c of s) {
        freq[c.charCodeAt(0) - 97]++;
    }

    const left = [];
    let middle = "";

    for (let i = 0; i < 26; i++) {
        while (freq[i] >= 2) {
            left.push(String.fromCharCode(97 + i));
            freq[i] -= 2;
        }

        if (freq[i] === 1) {
            middle = String.fromCharCode(97 + i);
        }
    }

    return left.join("") + middle + [...left].reverse().join("");
};