783. Minimum Distance Between BST Nodes

发表于 | 分类于 | |

783. Minimum Distance Between BST Nodes

题目描述

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 :

1
2
3
4
5
6
7
8
9
10
11
12
13
14
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.

题目大意

给定一个二叉搜索树，返回树中任意两个不同节点的最小差值。

解题思路

中序遍历树，计算最小差值。

代码

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
class Solution {
    func minDiffInBST(_ root: TreeNode?) -> Int {
        var pre = -1
        var dist = Int.max
        func minDiff(root: TreeNode?) {
            guard let tree = root else { return }
            if let left = tree.left {
                minDiff(root: left)
            }
            if pre >= 0 {
                dist = min(dist, tree.val - pre)
            }
            pre = tree.val
            if let right = tree.right {
                minDiff(root: right)
            }
        }
        minDiff(root: root)
        return dist
    }
}
0%