题解 | #二叉搜索树最小差值#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return int整型
     */
    public int minDifference (TreeNode root) {
        // write code here
        Stack<TreeNode> stack = new Stack<>();
        Queue<Integer> queue = new LinkedList<>();
        TreeNode node = root;
        while (null != node) {
            stack.push(node);
            node = node.left;
        }
        while (!stack.isEmpty()) {
            node = stack.pop();
            queue.add(node.val);
            if (null != node.right) {
                node = node.right;
                while (null != node) {
                    stack.push(node);
                    node = node.left;
                }
            }
        }
        int res = Integer.MAX_VALUE;
        int pre = Integer.MAX_VALUE;
        while (!queue.isEmpty()) {
            int val = queue.poll();
            res = Math.min(res, Math.abs(val - pre));
            pre = val;
        }
        return res;
    }
}