recursion with stack vs array example

gistfile1.txt

/**
 * Definition for binary tree
 * class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) {
 *      val = x;
 *      left=null;
 *      right=null;
 *     }
 * }
 */
public class Solution {
    // ArrayList<Integer> arr=new ArrayList<Integer>();
    // ArrayList<ArrayList<Integer>> returnList=new ArrayList<ArrayList<Integer>>();
    
    // public ArrayList<ArrayList<Integer>> pathSum(TreeNode A, int B) {
    //     calc(A,B,arr,returnList,0);
    //     return returnList;
        
    // }
    
    // public void calc(TreeNode A,int B,ArrayList<Integer> arr,ArrayList<ArrayList<Integer>> returnList,int j){
    //     if(A==null)
    //     return;
    //   arr.add(A.val);
    //       if(A.left == null && A.right == null) { 
    //         if(B==0){//adding result to list
    //         int idx=0;
            
    //       // System.out.println("START");
    //         //System.out.println(">"+num);
    //           returnList.add(new ArrayList<Integer>(arr));  
    //         }
                
            
    //     }
          
          
    //      calc(A.left,B-A.val,arr,returnList,j);
    //     calc(A.right,B-A.val,arr,returnList,j);
    //     arr.remove(arr.size()-1);
    //   //  System.out.println("START");
    //     //arr.forEach(x->System.out.println(x));
    //     //System.out.println("END");
      
    
        
    // }
    
    //THIS SOLUTION is from https://github.com/varunu28/InterviewBit-Java-Solutions/blob/master/Trees/Problems/Roots%20To%20Leaf%20Path%20Sum.java
    private ArrayList<ArrayList<Integer>> resultList = new ArrayList<>();
    
    public void pathSumInner(TreeNode root, int sum, Stack<Integer>path) {
        path.push(root.val);
        
        if(root.left == null && root.right == null) {
            if(sum == root.val) resultList.add(new ArrayList<Integer>(path));
        }
        
        if(root.left!=null) pathSumInner(root.left, sum-root.val, path);
        if(root.right!=null)pathSumInner(root.right, sum-root.val, path);
        
        path.pop();
        //      System.out.println("START");
        //  path.stream().forEach(x->System.out.println(x));
        //  System.out.println("END");
    }
    
    public ArrayList<ArrayList<Integer>> pathSum(TreeNode root, int sum) {
        if(root==null) return resultList;
        Stack<Integer> path = new Stack<Integer>();
        pathSumInner(root, sum, path);
        return resultList;
    }
}