二分查找参数解释和查询原理:
二分查找的前提是列表有序,下面以升序列表为例,order_list为有序列表,key为需要查找的值,left和right在列表或数组中相当于左右下标,表示在数组或列表的 [left, right] 范围内查找,查找过程中不断缩小 [left, right] 覆盖的范围,直到查找成功返回下标,不成功返回None。下面给出了循环和递归实现。
循环实现二分查找:
# 用循环实现二分查找
a = [1, 3, 4, 6, 7, 8, 9, 11, 15, 17, 19, 21, 22, 25, 29, 33, 38, 69, 107]
user_input = int(input("请输入你要查询的值:"))
def while_half_search(order_list, key, left, right):
while left <= right:
mid = (left + right) # 循环里面一定要有修改变量的值
if key > order_list[mid]:
left = mid + 1
elif key < order_list[mid]:
right = mid - 1
else:
return mid
return None
left = 0
right = len(a) - 1
result = while_half_search(a, user_input, left, right)
print(result)
递归实现二分查找:
# 用递归实现2分查找的算法
a = [1, 3, 4, 6, 7, 8, 9, 11, 15, 17, 19, 21, 22, 25, 29, 33, 38, 69, 107]
# print(len(a))
user_input = int(input("请输入你要查询的值:"))
def HalfSearch(OrderedList, key, left, right):
if left > right:
return None
mid = (left + right) // 2
if key == OrderedList[mid]:
return mid
elif key > OrderedList[mid]:
return HalfSearch(OrderedList, key, mid + 1, right)
else:
return HalfSearch(OrderedList, key, left, mid - 1)
left = 0
right = len(a) - 1
index = HalfSearch(a, user_input, left, right)
print(index)