leetcode-783-Minimum-Distance-Between-BST-Nodes

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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 :

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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:

  1. The size of the BST will be between 2 and 100.
  2. The BST is always valid, each node’s value is an integer, and each node’s value is different.

分析

要找最小的差值，如果序列是有序的，直接找最小的相邻的两个节点的差值即可。中序遍历的序列刚好是有序的。

解决方案1(Java)

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    Integer result = Integer.MAX_VALUE, pre = null;
    public int minDiffInBST(TreeNode root) {
        if (root.left != null) {
            minDiffInBST(root.left);
        }
        if (pre != null) {
            result = Math.min(result, root.val - pre);
        }
        pre = root.val;
        if (root.right != null) {
            minDiffInBST(root.right);
        }
        return result;
    }
}

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