39 Combination Sum – Medium

Problem:

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]

Thoughts:

Idea is to use a modified DFS.

Solutions:

public class Solution {
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        if(candidates == null || candidates.length == 0) return result;
        ArrayList<Integer> current = new ArrayList<Integer>();
        Arrays.sort(candidates);
        combinationSum(candidates, target, 0, current, result);
        return result;
    }
    public void combinationSum(int[] candidates, int target, int j, ArrayList<Integer> curr, List<List<Integer>> result){
        if(target == 0){
            ArrayList<Integer> temp = new ArrayList<Integer>(curr);
            result.add(temp);
            return;
        }
        for(int i=j; i<candidates.length; i++){
            if(target < candidates[i])
                return;
            curr.add(candidates[i]);
            combinationSum(candidates, target - candidates[i], i, curr, result);
            curr.remove(curr.size()-1);
       }//for i
   }//combinationSum
}//Solution