二叉树的递归套路

• 与根节点无关

• 经过根节点 ```java public class TreeNode {

  int val;
  TreeNode left;
  TreeNode right;

  }

  public class Info {

    public int maxDistance;
    public int height;
    public Info(int maxDistance, int height) {
        this.maxDistance = maxDistance;
        this.height = height;
    }

  }

  public int diameterOfBinaryTree(TreeNode root) {

    return process(root).maxDistance;

  }

  public Info process(TreeNode node) {

    if (node == null) {
        return new Info(0, 0);
    }
    Info leftInfo = process(node.left);
    Info rightInfo = process(node.right);
    // 不经过根节点
    int p1 = Math.max(leftInfo.maxDistance, rightInfo.maxDistance);
    // 经过根节点
    int p2 = leftInfo.height + rightInfo.height;
    int height = Math.max(leftInfo.height, rightInfo.height) + 1;
    return new Info(Math.max(p1, p2), height);

  } }

```