【LeetCode】Path Sum II

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]
]

public class Solution {
    public ArrayList<ArrayList<Integer>> pathSum(TreeNode root, int sum) {
        if(root==null)
            return re;
        ArrayList<Integer> init = new ArrayList<Integer>();
        int t=0;
        PreOrder(root,init,t,sum);
        return re;
        
    }
    public ArrayList<ArrayList<Integer>> re = new ArrayList<ArrayList<Integer>>();
    private void PreOrder(TreeNode root, ArrayList<Integer> init,int t,int sum) {
        if(root!=null){
            t+=root.val;
            init.add(root.val);
            if(t==sum){
                if(root.left==null&&root.right==null){
                    ArrayList<Integer> temp = new ArrayList<Integer>();
                    temp.addAll(init);
                    re.add(temp);
                }
            }
            
            PreOrder(root.left,init,t,sum);
            PreOrder(root.right,init,t,sum);
            t-=root.val;
            init.remove(init.size()-1);
        }
        
    }
    
    
}