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class Solution {
    static List<List<Integer>> ans;
    public List<List<Integer>> pathSum(TreeNode root, int targetSum) {
        if (root == null) return ans;
        ans=new ArrayList<>();
        dfs(new ArrayList<>(),root,0,targetSum);
        return ans;
    }

    public static void dfs(List<Integer> list,TreeNode node,int sum,int targetSum){
        if (node==null){
            return;
        }
        list.add(node.val);
        sum += node.val;
        
        if (node.left == null && node.right == null && sum == targetSum) {
            ans.add(new ArrayList<>(list)); // 这里一定要 new 一个副本
        }

        dfs(list,node.left,sum,targetSum);
        dfs(list,node.right,sum,targetSum);
        list.remove(list.size()-1);
    }
}