[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]

 

public class Solution {
List<List<Integer>> res;

public List<List<Integer>> combinationSum(int[] candidates, int target) {
res = new ArrayList<List<Integer>>();
Arrays.sort(candidates);
for (int i = 0; i < candidates.length; i++) {
List<Integer> list = new ArrayList<Integer>();
helper(candidates, list, i, 0, target);
}
return res;
}

public void helper(int[] candidates, List<Integer> list, int pos, int sum, int target) {
sum += candidates[pos];

if (sum > target) return;
else if (sum == target) {
list.add(candidates[pos]);
List<Integer> tmp = new ArrayList<Integer>(list);
res.add(tmp);
list.remove(list.size()-1);
return;
}
else {
list.add(candidates[pos]);
for (int i = pos; i < candidates.length; i++) {
helper(candidates, list, i, sum, target);
}
list.remove(list.size()-1);
}
}
}