class Solution {
  public List<List<Integer>> pathSum(TreeNode root, int sum) {
    List<List<Integer>> ans = new ArrayList<>();
    dfs(root, sum, new ArrayList<>(), ans);
    return ans;
  }

  private void dfs(TreeNode root, int sum, List<Integer> path, List<List<Integer>> ans) {
    if (root == null)
      return;
    if (root.val == sum && root.left == null && root.right == null) {
      path.add(root.val);
      ans.add(new ArrayList<>(path));
      path.remove(path.size() - 1);
      return;
    }

    path.add(root.val);
    dfs(root.left, sum - root.val, path, ans);
    dfs(root.right, sum - root.val, path, ans);
    path.remove(path.size() - 1);
  }
}