class Solution {
    public List<List<Integer>> pathSum(TreeNode root, int targetSum) {
        List<List<Integer>> res = new ArrayList<>();
        pathSum_0(root, targetSum, new ArrayList<>(), res);
        return res;
    }
    public void pathSum_0(TreeNode root, int targetSum, List<Integer> cur, List<List<Integer>> res) {
        if (root == null) return;
        cur.add(root.val);
        if (root.left == null && root.right == null && targetSum == root.val) { // 到根节点了
            res.add(new ArrayList<>(cur));
        } else { // 没到根节点
            pathSum_0(root.left, targetSum - root.val, cur, res);
            pathSum_0(root.right, targetSum - root.val, cur, res);
        }
        cur.remove(cur.size() - 1);
    }
}

class Solution {
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        List<List<Integer>> res = new LinkedList<>();
        if (root == null) return res;
        if (root.left == null && root.right == null) {
            if (root.val == sum) {
                List<Integer> r = new LinkedList<>();
                r.add(root.val);
                res.add(r);
            }
            return res;
        }
        List<List<Integer>> leftRes = pathSum(root.left, sum - root.val);
        List<List<Integer>> rightRes = pathSum(root.right, sum - root.val);
        leftRes.addAll(rightRes);
        for (List<Integer> path: leftRes) {
            path.add(0, root.val);
            res.add(path);
        }
        return res;
    }
}