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] 

package leetcode;

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

public class CombinationSum {
    public static List<List<Integer>> combinationSum(int[] candidates,
            int target) {
        Arrays.sort(candidates);
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        getResult(result, new ArrayList<Integer>(), candidates, target, 0);

        return result;
    }

    private static void getResult(List<List<Integer>> result,
            List<Integer> cur, int candidates[], int target, int start) {
        if (target > 0) {
            for (int i = start; i < candidates.length
                    && target >= candidates[i]; i++) {
                cur.add(candidates[i]);
                getResult(result, cur, candidates, target - candidates[i], i);
                cur.remove(cur.size() - 1);
            }// for
        }// if
        else if (target == 0) {
            result.add(new ArrayList<Integer>(cur));
        }// else if
    }

    public static void main(String[] args) {
        int[] nums = { 2, 3, 7 };
        System.out.println(combinationSum(nums, 7));

    }

}