Leetcode: 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.
• Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
• 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:

public class Solution {
    public List<List<Integer>> combinationSum(int[] candidates, int target)
    {
        List<List<Integer>> solution = new ArrayList<List<Integer>>();
        Arrays.sort(candidates);
        combinationSum (candidates, target, 0, 0, new ArrayList<Integer>(), solution );
        return solution;
    }
    
    public void combinationSum(int[] candidates, int target, int index, int sum, ArrayList<Integer> tillNow, List<List<Integer>> solution) 
    {
        if(sum == target)
        {
            solution.add((List<Integer>)tillNow.clone());
            return;
        }
        if(index==candidates.length)
        {
            return;
        }
        for(int i= index; i<candidates.length; i++)
        {
            if(sum+candidates[i]>target)
                break;
            tillNow.add(candidates[i]);
            combinationSum(candidates, target, i, sum+candidates[i], tillNow, solution);
            tillNow.remove(tillNow.size()-1);
        }
        
    }
}