老师你好。
我在做leetcode第377题时，想用dfs解决，但是怎么想backtrack的时候got stuck不知道咋做了，老师能帮看下么？
https://leetcode.com/problems/combination-sum-iv

class Solution {
    private int count;
    public int combinationSum4(int[] nums, int target) {
        Arrays.sort(nums);
        this.count = 0;
        _find(nums, target, 0);
        return count;
    }
    private void _find(int[] nums, int target, int start) {
        if (target == 0) {
            count++;
            return;
        }
        for (int i = start; i < nums.length; i++) {
            if(nums[i] > target) {
                break;
            }
            _find(nums, target - nums[i], i);
            //how to backtrack?
        }
    }
}