non-recur and recur for bst paths

LC257BSTPath.java

    public List<String> binaryTreePaths(TreeNode root) {
        //List<List<Integer>> ans = new ArrayList<>();
        // dfs(root, new ArrayList<>(), ans);
        // return formatAns(ans);

        List<String> ans = new ArrayList<>();
        dfsIter(root, ans);
        return ans;
    }
    
    private void dfsIter(TreeNode root, List<String> ans) {
        if (root == null) return;
        TreeNode p = root;
        Stack<String> path = new Stack<>();
        Stack<TreeNode> stk = new Stack<>();
        stk.push(p);
        path.push(String.valueOf(p.val));
        
        while (!stk.isEmpty()) {
            TreeNode cur = stk.pop();
            String tempPath = path.pop();
            if (cur.left == null && cur.right == null) {
                ans.add(new String(tempPath));
            }
            if (cur.right != null) {
                stk.push(cur.right);
                path.push(tempPath + "->" + cur.right.val);
            }
            if (cur.left != null) {
                stk.push(cur.left);
                path.push(tempPath + "->" + cur.left.val);
            }
        }
    }
    
    private List<Integer> getPath(Stack<TreeNode> stk) {
        Stack<TreeNode> copy = new Stack<>();
        List<Integer> ans = new ArrayList<>();
        while (!stk.isEmpty()) {
            copy.push(stk.pop());
        }
        while (!copy.isEmpty()) {
            TreeNode nd = copy.pop();
            stk.push(nd);
            ans.add(nd.val);
        }
        return ans;
    }
    
    private void dfs(TreeNode root, List<Integer> cur, List<List<Integer>> ans) {
        if (root == null) return;
        cur.add(root.val);
        if (root.left == null && root.right == null) ans.add(new ArrayList<>(cur));
        dfs(root.left, cur, ans);
        dfs(root.right, cur, ans);
        cur.remove(cur.size() - 1);
    }
    
    private List<String> formatAns(List<List<Integer>> ans) {
        List<String> res = new ArrayList<>();
        for (List<Integer> one : ans) {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < one.size(); i++) {
                sb.append(one.get(i));
                if (i != one.size() - 1) sb.append("->");
            }
            res.add(sb.toString());
        }
        return res;
    }