auto save

diy2.py

+import random
+
+alist = []
+for i in range(1, 101):
+    alist.append(i)
+num = random.choice(alist)
+# 请完善二分查找函数binary_search(),查找出num在列表alist里面的索引位置
+
+def binary_search(alist,num):
+    low = 0         # 初始最低索引
+    high = len(alist)-1          # 初始最高索引
+    while low <= high:      # 当最低索引小于等于最高索引
+        mid = (low + high) // 2
+        guess = alist[mid]
+        if guess == num:        # 中间值等于查找对象，返回索引
+            return mid
+        elif guess < num:       # 中间值小于查找对象
+            low = mid + 1
+        else:                   # 中间值大于查找对象
+            high = mid - 1
+    return None
+
+result = binary_search(alist, num)
+print("老师给的数是：", num)
+print("它在列表里的索引是：", result)       # 列表从1开始，索引从0开始，所以少1
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