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] 

 

 

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Solution {
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
    	List<List<Integer>> res = new ArrayList<List<Integer>>();  
        List<Integer> item = new ArrayList<Integer>();  
        if (candidates == null || candidates.length==0) {
        	return res;
        }
        Arrays.sort(candidates);
        solve(candidates,target, 0, item ,res);
        return res;
    }

	private void solve(int[] candidates, int target, int start, List<Integer> item,
			List<List<Integer>> res) {
		// TODO Auto-generated method stub
		if (target < 0) {
			return;
		}
		if (target == 0) {
			res.add(new ArrayList<>(item));
			return;
		}
		for (int j = start; j < candidates.length; j++) {
			if (j > 0 && candidates[j] == candidates[j-1]) {
				continue;
			}
			item.add(candidates[j]);
			solve(candidates,target-candidates[j], j, item ,res);
			item.remove(item.size()-1);
		}
	}
}