【算法】二叉排序树：创建二叉树，并以中序遍历输出

public class Node {
  private Node left;  // 左子节点
  private Node right;  // 右子节点
  private int data;  // 节点的值
  public Node(int data){
    this.left = null;
    this.right = null;
    this.data = data;
  }
  public Node getLeft() {
    return left;
  }
  public void setLeft(Node left) {
    this.left = left;
  }
  public Node getRight() {
    return right;
  }
  public void setRight(Node right) {
    this.right = right;
  }
  public int getData() {
    return data;
  }
  public void setData(int data) {
    this.data = data;
  }
}
// 以中序遍历的方式输出：
@Override
public String toString() {
  return (left == null?"":(left.toString() + ","))
      + data 
      + (right == null?"":("," + right.toString() ));
  }
}