leetcode 108: Combination Sum II

Combination Sum II Mar 7 '12

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, � , a_k) must be in non-descending order. (ie, a₁ ? a₂ ? � ? a_k).
• 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]

 

can not pass big test set.

public class Solution {
    HashSet<ArrayList<Integer>> unique = new HashSet<ArrayList<Integer>>();
    
    public ArrayList<ArrayList<Integer>> combinationSum2(int[] num, int target) {
        // Start typing your Java solution below
        // DO NOT write main() function
        unique.clear();
        ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
        
        //check input
        if(num==null || num.length==0 ) return res; 
        
        ArrayList<Integer> temp = new ArrayList<Integer>();
        
        Arrays.sort( num);
        comRec(num, res, temp, target, 0, 0);
        return res;
    }
    
    private void comRec(int[] num, ArrayList<ArrayList<Integer>> res, ArrayList<Integer> temp, int target, int partSum, int level){
        if(level > num.length) return;
        
        if(partSum == target ) {
            ArrayList<Integer> t = new ArrayList<Integer>(temp);
            if(!unique.contains(t)) {
                res.add(t);
                unique.add(t);
            }
            return;
        }
        
        for(int i=level; i<num.length; i++) {
            temp.add( num[i] );
            comRec(num, res, temp, target, partSum+num[i], i+1);
            temp.remove( temp.size()-1);
        }
    }
}