Permutation Problem

Permutation.java

import java.util.*;

class Permutation {
    public static void main(String[] args) {
        String[] dayHoursList = new String[]{"4", "4", "4", "4", "4", "?", "?"};
        int maxDayHours = 8;
        int weekHours = 28;
        List<String> results = getPermutation(dayHoursList, maxDayHours, weekHours);
        for(int i = 0; i < results.size(); i++) {
            System.out.println(results.get(i));
        }
    }

    public static List<String> getPermutation(String[] dayHoursList, int maxDayHours, int weekHours) {
        List<String> results = new ArrayList<>();
        int permutationNumber = 0;

        for(int i = 0; i < dayHoursList.length; i++) {
            if(dayHoursList[i].equals("?")) {
                permutationNumber ++;
            }
            else {
                weekHours -= Integer.parseInt(dayHoursList[i]);
            }
        }

        /* In the case, find 2 numbers which are not larger then 8.*/
        /* The sum of those 2 numbers should equal to 8 */
        /* {0,8}{1,7}{2,6}{3,5}{4,4}{5,3},{6,2},{7,1},{8,0} */

        List<List<Integer>> permuLists = new ArrayList<>();
        int[] nums = new int[maxDayHours + 1];
        for(int i = 0; i <= maxDayHours; i++) {
            nums[i] = i;
        }

        backtracking(permuLists, new ArrayList<>(), nums, 0, permutationNumber, weekHours);

        for(int i = 0; i < permuLists.size(); i++) {
            List<Integer> list = permuLists.get(i);
            int count = 0;
            StringBuilder sb = new StringBuilder();
            for(int j = 0; j < dayHoursList.length; j++) {
                if(dayHoursList[j].equals("?")) {
                    sb.append(list.get(count++));
                }
                else {
                    sb.append(dayHoursList[j]);
                }
            }
            results.add(sb.toString());
        }
        return results;
    }


    public static void backtracking(List<List<Integer>> list, List<Integer> tempList, int[] nums, int sum,
                                    int permutationNumber, int target) {
        if(tempList.size() == permutationNumber) {
            if(sum == target) {
                list.add(new ArrayList<>(tempList));
            }
            return;
        }
        for(int i = 0; i < nums.length; i++) {
            tempList.add(nums[i]);
            sum += nums[i];
            backtracking(list, tempList, nums, sum, permutationNumber, target);
            sum -= tempList.get(tempList.size() - 1);
            tempList.remove(tempList.size() - 1);
        }
    }
}