《算法图解》第四章第一节练习

4.1请编写前述sum函数的代码。

def diy_sum(arr):
if not arr:
    return 0
elif len(arr) == 1:
    return arr[0]
else:
    return arr.pop(0) + diy_sum(arr)


arr = [1, 2, 3]
print(diy_sum(arr))

4.2编写一个递归函数来计算列表包含的元素数。

def count_elements(list):
if not list:
    return None
elif len(list) == 1:
    return 1
else:
    return 1 + count_elements(list[1:])


list = [1, 2, 3]
print(count_elements(list))

4.3找出列表中最大的数字

def bigger(int1, int2):

if int1 >= int2:
    return int1
else:
    return int2

def find_biggest(list):

if not list:
    return None
elif len(list) == 1:
    return list[0]
elif len(list) == 2:
    return bigger(list[0], list[1])
else:
    return bigger(list[0], find_biggest(list[1:]))


list = [1, 5, 3, 2]
print(find_biggest(list))

4.4 还记得第1章介绍的二分查找吗？它也是一种分而治之算法。你能找出二分查找算法的基线条件和递归条件吗？

def binary_search_basic(list, target, low, high):
if low > high:
    return None
else:
    mid = int((low + high) / 2 + 0.5)
    guess = list[mid]
    if guess == target:
        return mid
    elif guess > target:
        high = mid - 1
        return binary_search_basic(list, target, low, high)
    else:
        low = mid + 1
        return binary_search_basic(list, target, low, high)


def binary_search_dc(list, target):
    return binary_search_basic(list, target, 0, len(list) - 1)

list = [1, 2, 3, 4, 5]
target = 3
print(binary_search_dc(list, target))

参考：
https://blog.csdn.net/XIAOZHI...