Custom Sort String

class Solution {
public:
    string customSortString(string order, string s) {
        int cnt[26] = {0};
        for (char c : s) ++cnt[c - 'a'];
        string ans;
        ans.reserve(s.size());
        for (char c : order) {
            int idx = c - 'a';
            ans.append(cnt[idx], c);
            cnt[idx] = 0;
        }
        for (int i = 0; i < 26; ++i) ans.append(cnt[i], 'a' + i);
        return ans;
    }
};

func customSortString(order string, s string) string {
    var cnt [26]int
    for _, c := range s {
        cnt[c-'a']++
    }
    ans := make([]byte, 0, len(s))
    for i := 0; i < len(order); i++ {
        c := order[i]
        idx := c - 'a'
        for k := 0; k < cnt[idx]; k++ {
            ans = append(ans, c)
        }
        cnt[idx] = 0
    }
    for i := 0; i < 26; i++ {
        for k := 0; k < cnt[i]; k++ {
            ans = append(ans, byte('a'+i))
        }
    }
    return string(ans)
}

from collections import Counter

class Solution:
    def customSortString(self, order: str, s: str) -> str:
        cnt = Counter(s)
        parts = []
        for c in order:
            if cnt[c]:
                parts.append(c * cnt[c])
                cnt[c] = 0
        for c, k in cnt.items():
            if k:
                parts.append(c * k)
        return ''.join(parts)

function customSortString(order, s) {
    const cnt = new Array(26).fill(0);
    const A = 'a'.charCodeAt(0);
    for (const c of s) cnt[c.charCodeAt(0) - A]++;
    const parts = [];
    for (const c of order) {
        const idx = c.charCodeAt(0) - A;
        if (cnt[idx]) {
            parts.push(c.repeat(cnt[idx]));
            cnt[idx] = 0;
        }
    }
    for (let i = 0; i < 26; i++) {
        if (cnt[i]) parts.push(String.fromCharCode(A + i).repeat(cnt[i]));
    }
    return parts.join('');
}

class Solution {
    public String customSortString(String order, String s) {
        int[] cnt = new int[26];
        for (int i = 0; i < s.length(); i++) cnt[s.charAt(i) - 'a']++;
        StringBuilder ans = new StringBuilder(s.length());
        for (int i = 0; i < order.length(); i++) {
            char c = order.charAt(i);
            int idx = c - 'a';
            for (int k = 0; k < cnt[idx]; k++) ans.append(c);
            cnt[idx] = 0;
        }
        for (int i = 0; i < 26; i++) {
            for (int k = 0; k < cnt[i]; k++) ans.append((char) ('a' + i));
        }
        return ans.toString();
    }
}

function customSortString(order: string, s: string): string {
    const cnt: number[] = new Array(26).fill(0);
    const A = 'a'.charCodeAt(0);
    for (const c of s) cnt[c.charCodeAt(0) - A]++;
    const parts: string[] = [];
    for (const c of order) {
        const idx = c.charCodeAt(0) - A;
        if (cnt[idx]) {
            parts.push(c.repeat(cnt[idx]));
            cnt[idx] = 0;
        }
    }
    for (let i = 0; i < 26; i++) {
        if (cnt[i]) parts.push(String.fromCharCode(A + i).repeat(cnt[i]));
    }
    return parts.join('');
}