Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

Each number in C may only be used once in the combination.

Note:

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

For example, given candidate set [10, 1, 2, 7, 6, 1, 5] and target 8, 
A solution set is: 

[
  [1, 7],
  [1, 2, 5],
  [2, 6],
  [1, 1, 6]
]

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注意：有重複元素，會導致出現相同集合

public class Solution {
    
    List<List<Integer>> result=new ArrayList<List<Integer>>();
    
    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
        if(candidates.length<=0){return result;}
        Arrays.sort(candidates);
        helper(new ArrayList(),candidates,0,target);
        return result;
    }
    public void helper(ArrayList<Integer> path,int [] candidates,int from,int target){
        if(target==0){
            List<Integer> list =new ArrayList<>(path);
            result.add(list);
        }else{
            int weiyi=Integer.MAX_VALUE;;//防止重複
            for(int i=from;i<candidates.length&&candidates[i]<=target;i++){
                
                if(candidates[i]!=weiyi){
                path.add(candidates[i]);
                helper(path,candidates,i+1,target-candidates[i]);
                weiyi=candidates[i];
                path.remove(path.size()-1);}
                
            }
        }
        
    }
}