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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
 # 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]
-low=0
-high=len(num_list)-1
+import random
+alist=[]
+for i in range(1,101):
+    alist.append(i)
+num=1#random.choice(alist)
+# num=60
+# low=0
+# high=len(alist)-1
 
 
 def b_s(alist,num):
 def b_s(alist,num):
     low=0
     low=0
     high=len(alist)-1
     high=len(alist)-1
+
     while low<=high: 
     while low<=high: 
-        guess=alist[mid]
         mid=(low+high)//2
         mid=(low+high)//2
-        num=alist[mid]
-    if guess==num:
-        print('找到了',mid)
-        break
-    elif guess<num:
-        high=mid-1
-    else:
-        low=mid+1
-        
-r=b_s(num_list,21)
-print(r)
+        guess=alist[mid]
+        if guess==num:
+            return mid
+        elif guess<num:
+            low=mid+1
+        else:
+            high=mid-1
+    return None
+result=b_s(alist,num)
+print("数",num)
+print("索引是",result)
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