技術標籤：資料結構二叉樹

前序排列：根左右，從主根開始

//遞迴
public static void preOrder(TreeNode root){
  if(root != null){
        Sysout.out.println(root.data + "");
        preOrder(root.lchild);
        preOrder(root.rchild);
    }
}

//前序遍歷---非遞迴
Stack<TreeNode> stack = new Stack<>();
List<TreeNode> list = new ArrayList<>();

public List<TreeNode> preOrder(TreeNode root){
	while(root!=null || !stack.isEmpty()){
		while(root!=null){
			list.add(root);
			stack.push(root);
			root=root.left;
		}
		TreeNode node = stack.pop();
		root = node.right;
	}
	return list;
}