Custom Sort String

题目
S and T are strings composed of lowercase letters. In S, no letter occurs more than once.

S was sorted in some custom order previously. We want to permute the characters of T so that they match the order that S was sorted. More specifically, if x occurs before y in S, then x should occur before y in the returned string.

Return any permutation of T (as a string) that satisfies this property.

答案

class Solution {
    public String customSortString(String S, String T) {
        int[] freq = new int[26];
        StringBuilder sb = new StringBuilder();
        for(char t : T.toCharArray()) {
            freq[t - 'a']++;
        }
        
        for(char s : S.toCharArray()) {
            for(int i = 0; i < freq[s - 'a']; i++)
                sb.append(s);
            freq[s - 'a'] = 0;
        }
        
        for(int i = 0; i < freq.length; i++) {
            int f = freq[i];
            for(int j = 0; j < f; j++)
                sb.append((char)('a' + i));
        }
        return sb.toString();
    }
}