Minimum Distance Between BST Nodes

题目

Given a Binary Search Tree (BST) with the root noderoot, return the minimum difference between the values of any two different nodes in the tree.

Example :

Input:  root = [4,2,6,1,3,null,null]

Output:  1

Explanation:

Note that root is a TreeNode object, not an array.

The given tree [4,2,6,1,3,null,null] is represented by the following diagram:

          4
        /   \
      2      6
     / \    
    1   3  

while the minimum difference in this tree is 1, it occurs between node 1 and node 2, also between node 3 and node 2.

分析：

乍一看没有什么思路，被题目中的‘任意两个node‘给唬住了，其实仔细想一想BST的特点就知道，其实BST中两个node最小的diff必然发生在root节点和它的左节点或者右节点