利用python通过循环和递归实现列表的二分查找

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)