LeetCode刷题--Minimum Distance Between BST Nodes

题目

原题地址

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.

答题

采用中序排序后，就可以得到一个排序好的数组，最小值肯定是数组相邻两个值之差。

private int minDis = -1;

public int minDiffInBST(TreeNode root) {
    List list = new ArrayList();
    print(root, list);
    int size = list.size();
    for (int i = 0; i < size - 1; i++) {
        int val = Math.abs(list.get(i) - list.get(i + 1));
        minDis = (minDis == -1) ? val : Math.min(val, minDis);
    }
    return minDis;
}

public void print(TreeNode node, List list) {
    if (node == null) {
        return;
    }
    print(node.left, list);
    list.add(node.val);
    print(node.right, list);
}