Combination Sum

Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

The same repeated number may be chosen from C unlimited number of times.

Note:

• All numbers (including target) will be positive integers.
• The solution set must not contain duplicate combinations.

For example, given candidate set [2, 3, 6, 7] and target 7, A solution set is:

[
  [7],
  [2, 2, 3]
]

Solution: (DP)

public class Solution {
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        Arrays.sort(candidates);
        HashMap<Integer, ArrayList<List<Integer>>> map = new HashMap<>();
        map.put(0,new ArrayList<List<Integer>>());
        map.get(0).add(new ArrayList<Integer>());
        ArrayList<List<Integer>> sum = new  ArrayList<List<Integer>>();
        for(int i = 1; i <= target; i++){
            sum = new  ArrayList<List<Integer>>();
            for(int option: candidates){
                if(i-option >= 0){
                   ArrayList<List<Integer>> temp = map.get(i-option);
                   if(temp != null){       
                       for(List<Integer> t: temp){
                         List<Integer> t2 = new ArrayList<Integer>();
                         t2.addAll(t);
                         t2.add(option);
                         Collections.sort(t2);
                         if(!sum.contains(t2)) sum.add(t2);
                       }
                   }
                }
                else break;
            }

            map.put(i, sum);
          }

        return sum;
    }
}