Custom Sort String

给一个字符串是序列的order, 求排序一个字符串.

class Solution {
    public String customSortString(String order, String s) {
        Map<Character, Integer> m = new HashMap<>();
        int k = 100;
        for(char c : order.toCharArray())
            m.put(c, k--);
        List<Character> list = new ArrayList<>();
        for(char c : s.toCharArray())
            list.add(c);
        Collections.sort(list, (a,b) ->{
            int aa = m.getOrDefault(a, Integer.MAX_VALUE / 2);
            int bb = m.getOrDefault(b, Integer.MAX_VALUE / 2);
            return bb - aa;
        });
        StringBuilder sb = new StringBuilder();
        for(char c : list)
            sb.append(c);
        return sb.toString();
    }
}