dfs

import java.util.*;
public class Solution {
     ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
     ArrayList<Integer> out = new ArrayList<Integer>();
    public ArrayList<ArrayList<Integer>> combinationSum2(int[]candidates , int target) {
         if(candidates == null || candidates.length <= 0) return null;
        Arrays.sort(candidates);
        dfs(candidates,target,0);
        return res;
    }
     public  void dfs(int[] candidates,int target, int start){
          if(target == 0){//找到一个合法解
                res.add(new ArrayList<>(out));//new为深拷贝，不会改变原来的值，不new会改变原来的值
                return;
              }
         
          for (int i = start; i < candidates.length; i++){
              
              if (i > start && candidates[i] == candidates[i - 1]) continue;
              target-=candidates[i];
              if(target < 0) {
               //target+=candidates[i];//为什么有没有这一行都能通过呢？？？内存占用变多了

                  return ;  
              }
             
            out.add(candidates[i]);            //执行扩展动作
            dfs(candidates,target,i+1);
            target+=candidates[i];
            out.remove(out.size()-1);         //撤销扩展动作
          }
     }
}