待解决)leetcode 路径和 dfs 线序遍历

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

For example:
Given the below binary tree and sum = 22,

              5
             / 
            4   8
           /   / 
          11  13  4
         /      / 
        7    2  5   1

return

[
   [5,4,11,2],
   [5,8,4,5]
]

1。下面的搜索总超时，可能我写的不好

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    ArrayList<ArrayList<Integer>> list=new ArrayList<ArrayList<Integer>>();
     ArrayList<Integer> arry=new ArrayList<Integer>();
     
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        
        if(root==null) return (List)list;
        if(root.right==null&&root.left==null)
        {
            if(sum==root.val)
            {
            
            list.add(new ArrayList(arry));
            }
        }
       
           arry.add(root.val);
        pathSum(root.right,sum-root.val);
      
        
        pathSum(root.left,sum-root.val);
        
        
        return (List)list;
        
       
       
        
        
    }
    
    
    
}