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binary_search.py

 # 使用二分查找法，找出9和20在列表里面的索引
-num = 1
+num = 4
 
 num_list = [1, 3, 5, 8, 11, 15, 17, 18, 20, 21]
 
@@ -15,4 +15,8 @@ while low <= high:
         low = mid + 1
     else:
         high = mid - 1
+
+
+if high < low:
+    print("不存在")
         
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