/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    //定義結果集 res 和 儲存路徑的集合 path
    List<List<Integer>> res = new ArrayList<>();
    LinkedList
 
<Integer> path = new LinkedList<>();

    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        recur(root,sum);
        return res ;
    }

    void  recur(TreeNode root,int tar){
        if(root == null) return;
        
        path.add(root.val);
        tar 
 
= tar - root.val;
        //如果當前節點已經是葉節點 並且 當前路徑和 為目標值，返回這一條路徑
        if(root.left == null && root.right == null && tar == 0){
            res.add(new ArrayList(path));
        }
        //遞迴呼叫左右子樹
        recur(root.left,tar);
        recur(root.right,tar);
        path.removeLast();
    }
}