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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
 b = [1, 3, 5, 8, 11, 15, 17, 18, 20, 21]
-k=0
-z=9
-f=9
-g=20
-while k<=z:
-    a=(k+z)//2
-    m = b[a]
-    if b[a]=f:
-        print(b[a])
+def n(alist,num):
+
+    a=0
+    c=20
+    d= len(b)-1
+    while a<d:
+        f=(a+d)//2
+        e=alist[f]
+        if e==num:
+            print(f)
             break
-    elif m<f: 
-        k=a+1
-    else:
-        k=a-1
-while k<=z:
-    e=(k+z)//2
-    m = b[a]
-    if b[a]=f:
-        print(b[a])
-        break
-    elif m<f: 
-        k=a-1
-    else:
-        k=a+1
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+        elif e<num: 
+            a=f+1
+        elif e>num:
+            a=f-1
+    return None
+result = n(b,21)
+print(result)
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