leetcode 39. Combination Sum

Given a set of candidate numbers (C) (without duplicates) 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.
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]
]

主要的思路是这一次是用这个数字还是不用这个数字
import java.util.LinkedList;
import java.util.List;


public class Solution39 {
    public static List<List<Integer>> ans = new LinkedList<List<Integer>>();
    public static LinkedList<Integer> list = new LinkedList<Integer>();
    public static void robot(int idx,int c[],int target){
        if (target==0) {
            System.out.println(list);
            List<Integer> list2 = new LinkedList<Integer>();
            for (Integer i : list) {
                list2.add(i);
            }
            ans.add(list2);
            return;
        }
        if (target<0||idx>=c.length) {
            return;
        }
        list.add(c[idx]);
        robot(idx, c, target-c[idx]);
        list.pollLast();
        robot(idx+1, c, target);
    }
    
    public static void main(String[] args) {
        int arr[]={2, 3, 6, 7};
        robot(0, arr, 7);

    }

}