# Combination Sum

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

Thesamerepeated 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]
]
``````

## Solution

Backtracking

``````class Solution {
public List<List<Integer>> combinationSum(int[] candidates, int target) {
List<List<Integer>> ans = new ArrayList<>();

Arrays.sort(candidates);

helper(target, 0, 0, candidates, new ArrayList<>(), ans);

return ans;
}

private void helper(int target, int sum, int startIdx, int[] candidates,
List<Integer> combo, List<List<Integer>> ans) {
if (sum == target) {
return;
}
if (sum > target) {
return;
}

for (int i = startIdx; i < candidates.length; i++) {