Python |计数范围内的设置位
原文:https://www.geeksforgeeks.org/python-count-set-bits-range/
给定一个非负数 n 和两个值 l 和 r 。问题是在 n 的二进制表示中对 l 到 r 范围内的置位位数进行计数，即从最右边的 lth 位计数到最右边的 rth 位。
约束: 1 < = l < = r < =二进制表示中的位数 n 。
示例:
Input : n = 42, l = 2, r = 5
Output : 2
(42)<sub>10</sub> = (101010)2
There are '2' set bits in the range 2 to 5.
Input : n = 79, l = 1, r = 4
Output : 4
这个问题我们已经有了解决方案，请参考在一定范围内计数设置位链接。我们可以用 Python 快速解决这个问题。方法很简单，
- Use the bin (num) function to convert decimal to binary.
- Now delete the first two characters of the output binary string, because by default, the bin function appends' 0b' to the output string as a prefix.
- Starting from index (l-1) , the string is sliced into index r and inverted, and then the setting bits in the middle are counted.
# Function to count set bits in a range
def countSetBits(n,l,r):
# convert n into it's binary
binary = bin(n)
# remove first two characters
binary = binary[2:]
# reverse string
binary = binary[-1::-1]
# count all set bit '1' starting from index l-1
# to r, where r is exclusive
print (len([binary[i] for i in range(l-1,r) if binary[i]=='1']))
# Driver program
if __name__ == "__main__":
n=42
l=2
r=5
countSetBits(n,l,r)
输出:
2
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