Minimum Distance Between BST Nodes

最新推荐文章于 2021-07-26 17:13:33 发布

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最新推荐文章于 2021-07-26 17:13:33 发布

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本文介绍了一种在二叉搜索树中找到任意两个不同节点之间最小差值的方法。通过两种不同的中序遍历策略实现，第一种将遍历结果存储在列表中再寻找最小差值；第二种直接在遍历过程中更新最小差值。

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Minimum Distance Between BST Nodes

Description

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:

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.

Tags: Tree

解读题意

给定一个查找二叉树，找出该树中结点与结点间相减的最小值。

思路1

用中序遍历得到一个有序的数组，遍历数组找出相邻最小值即可。

class Solution {

    public int minDiffInBST(TreeNode root) {

        List<Integer> tempList = new ArrayList<>();

        int distance = Integer.MAX_VALUE;
        minDiffInBSTHelper(root,tempList);

        for (int i = 1; i < tempList.size(); i++) {
            distance = Math.min(distance,tempList.get(i)-tempList.get(i-1));
        }

        return distance;
    }

     private void minDiffInBSTHelper(TreeNode root, List<Integer> vals) {

        if (root == null)
            return;

        minDiffInBSTHelper(root.left, vals);
        vals.add(root.val);
        minDiffInBSTHelper(root.right, vals);

    }

}

time complexity:O(n)

思路2

与思路1一致，但是可以通过定义两个类变量而不用创建数组。

public class Solution1 {

    private int distance = Integer.MAX_VALUE;

    private Integer pre ;

    public int minDiffInBST(TreeNode root) {
        pre = null;

        if (root == null)
            return 0;

        minDiffInBSTHelper(root);

        return distance;
    }

    private void minDiffInBSTHelper(TreeNode root) {

        if (root == null)
            return;

        minDiffInBSTHelper(root.left);
        if(pre != null)
            distance = Math.min(distance, root.val - pre);

        pre = root.val;
        minDiffInBSTHelper(root.right);
    }

}