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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.
Note:
- The size of the BST will be between 2 and
100. - The BST is always valid, each node's value is an integer, and each node's value is different.
# Definition for a binary tree node. # class TreeNode(object): # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution(object): def minDiffInBST(self, root): """ :type root: TreeNode :rtype: int """ # traverse node from min to max self.last_node = None self.min_diff = float('inf') def dfs(node): if not node: return dfs(node.left) if self.last_node: self.min_diff = min(self.min_diff, node.val-self.last_node.val) self.last_node = node dfs(node.right) dfs(root) return self.min_diff
# Definition for a binary tree node. # class TreeNode(object): # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution(object): def minDiffInBST(self, root): """ :type root: TreeNode :rtype: int """ # traverse node from min to max last_node = None ans = float("inf") node = root stack = [] while node: stack.append(node) node = node.left while stack: node = stack.pop() if last_node: ans = min(ans, node.val-last_node.val) last_node = node node = node.right while node: stack.append(node) node = node.left return ans
Morris Traversal:
# Definition for a binary tree node. # class TreeNode(object): # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution(object): def minDiffInBST(self, root): """ :type root: TreeNode :rtype: int """ # traverse node from min to max last_node = None ans = float("inf") cur = root while cur: if cur.left is None: if last_node: ans = min(ans, cur.val-last_node.val) last_node = cur cur = cur.right else: tmp = cur.left while tmp.right and not (tmp.right is cur): tmp = tmp.right if not tmp.right: tmp.right = cur cur = cur.left else: tmp.right = None if last_node: ans = min(ans, cur.val-last_node.val) last_node = cur cur = cur.right return ans
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