39. Combination Sum

Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.

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

Note:

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

Example 1:

Input: candidates = [2,3,6,7], target = 7,
A solution set is:
[
  [7],
  [2,2,3]
]

Example 2:

Input: candidates = [2,3,5], target = 8,
A solution set is:
[
  [2,2,2,2],
  [2,3,3],
  [3,5]
]

class Solution {
    
    public void dfs(List<List<Integer>> ans, int []candidates, int pos, int target, ArrayList<Integer> temp) {
        if (target == 0) {
            
            
            ans.add(new ArrayList<>(temp));
           
            return;
        }
        if (target < candidates[pos]) {
            return;
        }
        int n = candidates.length;
        System.out.println(pos);
        for (int i = pos; i < n && candidates[i] <= target; ++i) {
            temp.add(candidates[i]);
            dfs(ans, candidates, i, target - candidates[i],  temp);
            temp.remove(temp.size() - 1);
        }
    }
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        Arrays.sort(candidates);
        List<List<Integer>> ans = new ArrayList<>();
        if (candidates.length == 0) return ans;
        int n = candidates.length;
        ArrayList<Integer> temp = new ArrayList<>();
        dfs(ans, candidates, 0, target, temp);
        return ans;
    }
}