L791.java

import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

class Solution791 {
    class Solution {
        /**
         * 791. Custom Sort String https://leetcode.com/problems/custom-sort-string/description/
         *
         * @param S String
         *          A string representing order of characters for sorting
         * @param T String
         *          Input string to sort based on given order
         * @return Final result string
         * @timeComplexity O(n log n) Where n is the length of String T
         * @spaceComplexity O(1)
         */
        public String customSortString(String S, String T) {
            List<Character> chars = T.chars().mapToObj(c -> (char) c).collect(Collectors.toList());
            // We create a new comparator and sort the input string based on this comparator
            Collections.sort(chars, Comparator.comparingInt(c -> S.indexOf(c)));
            return chars.stream().map(String::valueOf).collect(Collectors.joining());
        }
    }
}