Sum List Recursively

递归求列表和

≈ 15 min · python-recursion python-lists · Open in WolfCode

Apply the same shape to a list instead of a number. Shorter list = smaller problem.

Python · runnable

def sum_list(t):
    if not t:                       # base case: empty list
        return 0
    return t[0] + sum_list(t[1:])   # recursive case

print(sum_list([]))                # 0
print(sum_list([5]))               # 5
print(sum_list([1, 2, 3]))         # 6
print(sum_list([10, 20, 30, 40]))  # 100

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The same shape, more variations

Python · runnable

def max_list(t):
    if len(t) == 1: return t[0]
    rest_max = max_list(t[1:])
    return t[0] if t[0] > rest_max else rest_max

def list_length(t):
    if not t: return 0
    return 1 + list_length(t[1:])

def reverse_list(t):
    if not t: return []
    return reverse_list(t[1:]) + [t[0]]

print(max_list([3, 1, 4, 1, 5, 9, 2, 6]))
print(list_length(["a", "b", "c", "d"]))
print(reverse_list([1, 2, 3, 4]))

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