题解 | #牛群最小体重差#

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
     *二叉搜索书的中序遍历为升序，所以按照中序遍历只需要计算相邻两个节点的差值，记录最小值即可。
     * 
     * @param root TreeNode类 
     * @return int整型
     */
    public int getMinimumDifference (TreeNode root) {
       Stack<TreeNode> stack = new Stack<>();
       int last = -100000;
       int min = 1000000;
       TreeNode node = root;
        while(!stack.isEmpty() || node != null){
            if(node != null){
                stack.push(node);
                node = node.left;
            }else {
                TreeNode temp = stack.pop();
                min = Math.min(min,temp.val-last);
                last = temp.val;
                node = temp.right;
            }
        }
       return min;
    }
}