一段代码让你理解二叉树的递归奥秘

class  TreeNode
{
TreeNode left;
TreeNode right;
int val;
TreeNode(int val){
this.val=val;
}
static void scanNodes(TreeNode root){
if(root!=null){
System.out.println("this is node :"+root.val); //先序遍历
scanNodes(root.left);
System.out.println("node"+root.val+" finish scanning left");
scanNodes(root.right);
System.out.println("node"+root.val+" finish scanning right");
}
}

public static void main(String[] args)
{
TreeNode root=new TreeNode(1);
TreeNode left1=new TreeNode(2);
TreeNode left2=new TreeNode(3);
TreeNode right1=new TreeNode(4);
//创建一棵树
root.left=left1;
left1.right=left2;
root.right=right1;
scanNodes(root);
}
}