[英]How to count the total number of set bits for the number
A = 3
DECIMAL BINARY SET BIT COUNT
1 01 1
2 10 1
3 11 2
1 + 1 + 2 = 4
Code is below代码如下
def solve(A):
ad = ''
for i in range(A + 1):
ad += str(bin(i).replace('ob',''))
return ad.count('1')
With Bit-wise按位
def solve(A):
count = 0
for i in range(A + 1):
while i > 0:
i= i & (i-1)
count += 1
return (count)
Time Limit Exceeded.
在这两种情况下,我都Time Limit Exceeded.
This would work in O(log(A)) so you shouldn't have Time Limit Exceeded:这将在 O(log(A)) 中工作,所以你不应该超过时间限制:
def solve(A):
count = 0
n = A
i = 0
while n > 0:
if (n & 1) == 1:
f = ((1 << i) >> 1) * i
g = (((1 << i) - 1) & A) + 1
count += f + g
n >>= 1
i += 1
return count
The total number of set bits between 0 and 2^n excluded is 2^(n-1)*n.排除在 0 和 2^n 之间的设置位总数为 2^(n-1)*n。 Because in this particular case, 50% of bits are set in each column and other 50% are unset, and there is n columns.因为在这种特殊情况下,每列中设置了 50% 的位,其他 50% 未设置,并且有 n 列。
For a number A which is not a power of 2, we can break down the calculation into several passes, one for each set bit in the number A in question, and use the expression for exact power of 2 (variable f).对于不是 2 的幂的数字 A,我们可以将计算分解为几遍,一次针对所讨论的数字 A 中的每个设置位,并使用 2 的精确幂(变量 f)的表达式。 We must also take care of an additional column of 1 each time (variable g).我们还必须每次都处理一个额外的 1 列(变量 g)。
I was working on a solution similar to covstag's one, but my way of calculating the sum of bits set for a power of 2 was definitely clumsier.我当时正在研究一种类似于 covstag 的解决方案,但我计算 2 的幂的位总和的方法肯定比较笨拙。 So I stole the idea and adapted it to my solution;所以我偷了这个想法并将其改编为我的解决方案; the result is just slightly faster, but perhaps easier to understand:结果只是稍微快一点,但也许更容易理解:
def solve(A):
loop = 0
current = 0
bits = f'{A:b}'
expo = len(bits) - 1
for b in bits[:-1]:
if b == '1':
power = 2**(expo-1)
current += expo * power + 1 + 2 * power * loop
loop += 1
expo -= 1
if bits[-1] != '0':
current += loop + 1
return current
This would work:这会起作用:
def solve(A):
return sum(int(b) for n in range(1, A + 1) for b in f"{n:b}" if b == '1')
This is another, very classic, way:这是另一种非常经典的方式:
def solve(A):
result = 0
for n in range(1, A + 1):
while n > 0:
result += n % 2
n //= 2
return result
In yours first solution, you can improve it a little:在您的第一个解决方案中,您可以稍微改进一下:
def solve(A):
result = 0
for i in range(A + 1):
result += bin(i).count('1')
return result
or even to甚至
def solve(A):
return sum(bin(i + 1).count('1') for i in range(A))
which is similar to my first attempt, maybe even better.这与我的第一次尝试相似,甚至可能更好。
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