1. class Solution {
  2.     public List<List<Integer>> combinationSum(int[] candidates, int target) {
  3.         List<List<Integer>> result = new ArrayList<>();
  4.         List<Integer> temp = new ArrayList<>();
  5.  
  6.         findCombinationSum(candidates, target, 0, result, temp);
  7.         return result;
  8.     }
  9.  
  10.     public void findCombinationSum(int[] nums, int target, int index, List<List<Integer>> result, List<Integer> temp)
  11.     {
  12.  
  13.         // Base condition 1: when target becomes 0
  14.         if(target == 0)
  15.         {
  16.             result.add(new ArrayList<>(temp));
  17.             return;
  18.         }
  19.  
  20.         // Base condition 2: when we reach end of the array
  21.         if(index == nums.length)
  22.             return;
  23.  
  24.         if(nums[index] <= target)
  25.         {
  26.             // pick the element 
  27.             temp.add(nums[index]);
  28.             findCombinationSum(nums, target - nums[index], index, result, temp);
  29.  
  30.             // do not pick the element
  31.             temp.remove(temp.size()-1);
  32.         }
  33.         findCombinationSum(nums, target, index+1, result, temp);
  34.         return;
  35.     }
  36. }