530. Minimum Absolute Difference in BST

题目：

Given a binary search tree with non-negative values, find the minimum absolute difference between values of any two nodes.

Example:

Input:

   1
    \
     3
    /
   2

Output:
1

Explanation:
The minimum absolute difference is 1, which is the difference between 2 and 1 (or between 2 and 3).

 

Note: There are at least two nodes in this BST.

链接：https://leetcode.com/problems/minimum-absolute-difference-in-bst/#/description

3/31/2017

16ms, 79%

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int getMinimumDifference(TreeNode root) {
        ArrayList<Integer> list = new ArrayList<Integer>();
        inOrderTraversal(root, list)        ;
        int minDiff = Integer.MAX_VALUE;

        for(int i = 1; i < list.size(); i++) {
            if (list.get(i) - list.get(i - 1) < minDiff) minDiff = list.get(i) - list.get(i - 1);
        }
        return minDiff;
    }
    private void inOrderTraversal(TreeNode root, ArrayList<Integer> list) {
        if (root == null) return;
        inOrderTraversal(root.left, list);
        list.add(root.val);
        inOrderTraversal(root.right, list);
    }
}

别人的解法，其中有关于BT的问题

https://discuss.leetcode.com/topic/80823/two-solutions-in-order-traversal-and-a-more-general-way-using-treeset

不需要用inorder traversal的方法，只需要跟前后值比较

https://discuss.leetcode.com/topic/80916/java-no-in-order-traverse-solution-just-pass-upper-bound-and-lower-bound

更多讨论：

https://discuss.leetcode.com/category/680/minimum-absolute-difference-in-bst