LeetCode39:组合总和

class Solution {
   
   public List> combinationSum(int[] candidates, int target) {
        //创建结果数组
       List> ans = new ArrayList<>();

       //调用回溯方法
       backtrack(0,candidates,target,new ArrayList<>(),ans);
       return ans;

   }

   //回溯方法
   private void backtrack(int start,int[] candidates,int target, ArrayList track,List> ans){
       if(target < 0){
           return;
       }
       //满足条件
       if(target == 0){
           ans.add(new ArrayList<>(track));
           
       }

       //选择列表
       for(int i = start;i < candidates.length;i++){
           //做选择
           track.add(candidates[i]);
           //回溯
           backtrack(i,candidates,target-candidates[i],track,ans);

           //撤销选择
           track.remove(track.size()-1);

       }

   }
}