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
-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 binary_search(list,item):
+    low = 0  # 定义最小下标
+    high = len(list)-1   # 定义最大下标
+    while low <= high:   #while循环，保证可以遍历到指定区域的元素，直到被被寻找的值和中间值相等
+        mid = int((low + high)/2)    # 寻找数组的中间值
+        guess = list[mid]   # 获取列表最中间的元素
+        if guess == item:   
+            return mid  	# 进行条件判断，将中间值和被寻找的值进行比较，相等则返回该值
+        if guess > item:    
+            high = mid-1	# 如果被寻找的值小于中间值，则最大下标变化为中间值的前一个元素下标
+        else:
+            low = mid + 1   # 如果被寻找的值大于中间值，则最小下标变化为中间值的后一个元素下标
+    return None
+print(binary_search(num_list,7))  # 输入一个有序列表和一个被寻找的值
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