### 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.*;

/**
* Created by gzdaijie on 16/5/21
* DFS
*/
public class Solution {
public List<List<Integer>> combinationSum(int[] candidates, int target) {
List<List<Integer>> result = new ArrayList<List<Integer>>();
Arrays.sort(candidates);
ArrayList tmp = new ArrayList();
combination(candidates, target, result,tmp, 0, 0);
return result;

}

private void combination(int[] candidates, int target, List<List<Integer>> result, ArrayList<Integer> tmp, int k, int sum) {
if (sum == target) {
return;
}
int len = candidates.length;
for (int i = k; i < len; i++) {
// 小于目标值时，从i开始继续尝试，因为可以重复
if (sum + candidates[i] <= target) {