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?
我本能地这样做了:
sum(int(digit) for digit in str(number))
我在网上找到了这个:
sum(map(int, str(number)))
哪种方法最适合速度,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,但是你可以纯整数做,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
<小时>
没有增加分配的版本更快:
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
<小时>
> %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