762. Prime Number of Set Bits in Binary Representation

最新推荐文章于 2020-12-28 01:20:11 发布

原创最新推荐文章于 2020-12-28 01:20:11 发布 · 68 阅读

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本文探讨了在给定范围内，具有质数个1位的二进制表示数的数量问题。通过C++实现，介绍了如何判断一个数是否为质数，并计算一个整数的二进制表示中1的个数，最后统计给定范围内满足条件的数的总数。

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Given two integers L and R, find the count of numbers in the range [L, R] (inclusive) having a prime number of set bits in their binary representation.

(Recall that the number of set bits an integer has is the number of 1s present when written in binary. For example, 21 written in binary is 10101 which has 3 set bits. Also, 1 is not a prime.)

Example 1:

Input: L = 6, R = 10
Output: 4
Explanation:
6 -> 110 (2 set bits, 2 is prime)
7 -> 111 (3 set bits, 3 is prime)
9 -> 1001 (2 set bits , 2 is prime)
10->1010 (2 set bits , 2 is prime)

C++:

class Solution {
public:
    bool isPrime(int num)
     {
		if(num<=1)
		    return false;
        for(int i = sqrt(num); i>1; i--)
        {
            if(num%i == 0)
            {
                return false;
            }
        }
        return true;
    }

    int numberof1(int n)
    {
        int count=0;
        while(n)
        {
            n &= (n-1);
            count++;		
        }
        return count;
    }
    int countPrimeSetBits(int L, int R) {
        int res=0;
        for(int i=L;i<=R;i++)
        {
            int num = numberof1(i);
            if(isPrime(num))
            {
                res++;
            }
        }
        return res;
        
    }
};