Given a set of candidate numbers (C) (without duplicates) 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.
• 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
     
      
       > combinationSum(int[] candidates, int target) {        List
       
        
         > result = new ArrayList
         
          
           >(); if(candidates == null || candidates.length == 0) { return result; } List
           
             list = new ArrayList
            
             (); Arrays.sort(candidates); helper(result, list, candidates, target, 0); return result; } public void helper(List
             
              
               > result, List
               
                 list, int[] nums, int remains, int position) { if(remains < 0) { return; } if(remains == 0) { result.add(new ArrayList
                
                 (list)); } for(int i = position; i < nums.length; i++) { list.add(nums[i]); helper(result, list, nums, remains - nums[i],i); list.remove(list.size() - 1); } } }