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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]
-num = 20
+num = 2
 low = 0
 low = 0
 high = len(num_list)-1
 high = len(num_list)-1
 while True:
 while True:
+    if high >= low:
         mid = (low+high)//2
         mid = (low+high)//2
         guess = num_list[mid]
         guess = num_list[mid]
         if guess == num:
         if guess == num:
@@ -13,3 +14,7 @@ while True:
             low = mid+1
             low = mid+1
         else:
         else:
             high = mid - 1
             high = mid - 1
+    else:
+        print("没找到")
+        break
+        
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