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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]
+num_list = [1, 3, 5, 8, 11, 15, 17, 18, 20, 21]
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+
+num = 20 #查找的数
+low = 0   #最低索引
+high = len(num_list)-1  #最大索引值
+
+while low <= high:
+    mid = (low+high) // 2  #中间索引值
+    guess = num_list[mid]  #猜测的数
+
+    if guess == num :
+        print('找到了索引是：',mid)
+        break
+    elif guess < num:
+        low = mid +1
+    else:
+        high = mid - 1
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