对一个数的位数求和

问题描述

如果我想找到一个数字的数字之和，即:

If I want to find the sum of the digits of a number, i.e.:

• 输入:932
• 输出:14，即(9 + 3 + 2)

最快的方法是什么?

我本能地做到了:

sum(int(digit) for digit in str(number))

我在网上找到了这个:

sum(map(int, str(number)))

哪个最适合用于速度，还有其他更快的方法吗?

Which is best to use for speed, and are there any other methods which are even faster?

推荐答案

你发的两行都很好，但你可以纯粹用整数来做，这样效率最高:

Both lines you posted are fine, but you can do it purely in integers, and it will be the most efficient:

def sum_digits(n):
    s = 0
    while n:
        s += n % 10
        n //= 10
    return s

或使用 divmod:

def sum_digits2(n):
    s = 0
    while n:
        n, remainder = divmod(n, 10)
        s += remainder
    return s

没有增强赋值的版本速度更快:

---

Even faster is the version without augmented assignments:

def sum_digits3(n):
   r = 0
   while n:
       r, n = r + n % 10, n // 10
   return r

> %timeit sum_digits(n)
1000000 loops, best of 3: 574 ns per loop

> %timeit sum_digits2(n)
1000000 loops, best of 3: 716 ns per loop

> %timeit sum_digits3(n)
1000000 loops, best of 3: 479 ns per loop

> %timeit sum(map(int, str(n)))
1000000 loops, best of 3: 1.42 us per loop

> %timeit sum([int(digit) for digit in str(n)])
100000 loops, best of 3: 1.52 us per loop

> %timeit sum(int(digit) for digit in str(n))
100000 loops, best of 3: 2.04 us per loop

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