class Solution {    public List
     
      
       > pathSum(TreeNode root, int sum) {        List
       
        
         > res=new ArrayList
         
          
           >(); pathSum(root, sum, new ArrayList
           
            (), res); return res; } private void pathSum(TreeNode node, int sum, List
            
              list, List
             
              
               > res){ if(node==null) return; list.add(node.val); if(node.left==null&&node.right==null) { if(node.val==sum) res.add(new ArrayList
               
                (list)); } else { if(node.left!=null) pathSum(node.left, sum-node.val, list, res); if(node.right!=null) pathSum(node.right, sum-node.val, list, res); } list.remove(list.size()-1); }}