Combination Sum II --- LeetCode

Combination Sum II

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Question Solution 

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.
• 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 10,1,2,7,6,1,5 and target 8, 
A solution set is: 
[1, 7] 
[1, 2, 5] 
[2, 6] 
[1, 1, 6] 

public class Solution {
    
    public List<List<Integer>> combinationSum2(int[] num, int target) {
         Set<List<Integer>> result=new HashSet<List<Integer>>();
    int len=num.length;
    if(len==0||num==null){
    return null;
    }
         Arrays.sort(num);
         Stack<Integer> stack=new Stack<Integer>();
         count(num,0,target,stack,result);         
    return new ArrayList<List<Integer>>(result);
    }

public void count(int [] num,int start,int target,Stack<Integer> stack,Set<List<Integer>> result){
if(target==0){
   @SuppressWarnings("unchecked")
List<Integer> tmp=(List<Integer>)stack.clone();
   result.add(tmp);
}
for(int i=start;i<num.length;i++){
 stack.push(num[i]);
 if(target-num[i]>=0){
 count(num,i+1,target-num[i],stack,result);
 }
 stack.pop();
}
}

}