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leetcode783

admin 11月 13, 2020 0

题目

Given a Binary Search Tree (BST) with the root node root, 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.

解答

这道题让我们求的是BST相邻节点的差的最小值，见到BST的时候，别忘了一个重要的性质就是BST在用中序遍历的时候得到的是个单调递增的数组，如上面的图得到的就是[1,2,3,4,6]，那么根据这个特点，这一类的题目就可以搞了。

class Solution:
    def minDiffInBST(self, root: TreeNode) -> int:
    
        res = []
        if not root:
            return 
        self.inorder(root, res)
        
        minimum = float('inf')
        for i in range(len(res)-1):
            minimum = min(res[i+1]-res[i], minimum)
        return minimum
    
    
    def inorder(self, root, res):
        if not root:
            return 
        
        self.inorder(root.left, res)
        res.append(root.val)
        self.inorder(root.right, res)
        