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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_list = [1, 3, 5, 8, 11, 15, 17, 18, 20, 21]
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+num_list = [1, 3, 5, 8, 11, 15, 17, 18, 20, 21]
+num=20
+low=0
+high=len(num_list)-1
+
+def binary_search(num_list,num):
+    low=0
+    high=len(num_list)-1
+
+    while low<high:
+        mid=(high+low)//2
+        guess=num_list[mid]
+        if num==guess:
+            return mid
+            
+        elif num>guess:
+            low=mid+1
+        else:
+            high=mid-1
+    return None
+
+result=binary_search(num_list,20)
+print(result)
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