save project

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]
-high = len(num_list) - 1
-num = 20
-low = 0
-while low <= high:
-    mid = (low + high) // 2
-    guess = num_list[mid]
-    if guess == num:
-        print("索引是:",mid)
-        break
-    elif guess < num:
-        low = mid + 1
-    elif guess > num:
-        high = mid - 1
-print(guess)
+
+def binary_search(alist, num):
+    low = 0
+    high = len(alist) - 1
+    while low <= high:
+        mid = (low + high) // 2
+        guess = alist[mid]
+        if guess == num:
+            return mid
+        elif guess < num:
+            low = mid + 1
+        elif guess > num:
+            high = mid - 1
+    return None
+
+a = print(binary_search(num_list,3 ))
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