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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]
+
+def chazhao(list1, n):
+    low = 0
+    high = len(list1) - 1
+
+    while high>=low:
+        mid = (low + high) //2
+        cai = list1[mid]
+        if cai == n:
+            return mid   #返回下标位置
+        elif cai < n:
+            low = mid + 1
+        else:
+            high = mid - 1
+    return -1  #表示没找到
+
+result = chazhao(num_list, 17)
+if result < 0:
+    print("没找到")
+else:
+    print("找到了，下标为"+str(result))
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