Update 0530.二叉搜索树的最小绝对差.md - 增加了python3版本的迭代解法

problems/0530.二叉搜索树的最小绝对差.md

@@ -222,6 +222,26 @@ class Solution:
         for i in range(len(res)-1):  // 统计有序数组的最小差值
             r = min(abs(res[i]-res[i+1]),r)
         return r
+        
+# 迭代法-中序遍历
+class Solution:
+    def getMinimumDifference(self, root: TreeNode) -> int:
+        stack = []
+        cur = root
+        pre = None
+        result = float('inf')
+        while cur or stack:
+            if cur: # 指针来访问节点，访问到最底层
+                stack.append(cur)
+                cur = cur.left
+            else: # 逐一处理节点
+                cur = stack.pop()
+                if pre: # 当前节点和前节点的值的差值
+                    result = min(result, cur.val - pre.val)
+                pre = cur
+                cur = cur.right
+        return result
+        
 ```
 Go：
 > 中序遍历，然后计算最小差值