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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]
-num=(9,20)
+num=9
 low=0
 high=len(num_list)
 guess=0
-for i in num:
-    while guess==num[i]:
-        mid=(low+high//2)
-        guess=num_list[mid]
-        if guess<num:low=mid+1
-        else:high=mid-1
-        if mid==low==high:
-            print(None)
-            break
-    print(mid)
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+while not num==guess:
+    mid=(low+high)//2
+    guess=num_list[mid]
+    if guess==num:
+        print(mid)
+        break
+    elif guess<num:low=mid+1
+    else:high=mid-1
+    if low==high:
+        print(None)
+        break
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