gold-4-6

设计一个算法，找出二叉搜索树中指定节点的“下一个”节点（也即中序后继）。

如果指定节点没有对应的“下一个”节点，则返回null。

示例 1:

输入: root = [2,1,3], p = 1

  2
 / \
1   3

输出: 2

示例 2:

输入: root = [5,3,6,2,4,null,null,1], p = 6

      5
     / \
    3   6
   / \
  2   4
 /   
1

输出: null

//leetcode submit region begin(Prohibit modification and deletion)
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    boolean isFound = false;

    public TreeNode inorderSuccessor(TreeNode root, TreeNode p) {
        return visitNext(root, p);
    }

    private TreeNode visitNext(TreeNode node, TreeNode p) {
        if (node == null) {
            return null;
        }

        TreeNode leftNode = visitNext(node.left, p);
        if (leftNode != null) {
            return leftNode;
        }

        if (isFound) {
            return node;
        }

        if (node == p) {
            isFound = true;
        }

        return visitNext(node.right, p);
    }
}
//leetcode submit region end(Prohibit modification and deletion)