Leetcode no. 39

39. 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 {    public List<List<Integer>> combinationSum(int[] candidates, int target) {        List<List<Integer>> res= new LinkedList<List<Integer>>();        List<Integer> lis= new LinkedList<Integer>();        if (candidates.length== 0) return res;        Arrays.sort(candidates);        combinationSum(candidates, target, res, lis, 0);        return res;    }    private void combinationSum(int[] candi, int target, List<List<Integer>> result, List<Integer> list, int start){        if (target==0) result.add(new LinkedList<>(list));        for (int i = start; i < candi.length; i++) {            if (target < candi[i]) break;            list.add(candi[i]);            combinationSum(candi, target-candi[i], result, list, i);            list.remove(list.size()-1);        }    }}