Tech Base

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.)

 

首先就是要先將 L 到 R 中間的數字轉為二進位表示，接著再根據轉換後有幾個 1 來得到 count，

最後再判斷 count 是否為質數，最後再回傳總共有幾個 count 為質數。

class Solution {
    public int countPrimeSetBits(int L, int R) {
        int count = 0;
        for(int i=L; i<=R; i++) {
            if(isLegal(i)) count++;
        }
        
        return count;
    }
    
    private boolean isLegal(int number) {
        int count = 0;
        char[] binaryNums = Integer.toBinaryString(number).toCharArray();
        for(char binaryNum : binaryNums) {
            if(binaryNum == '1') count++;
        }
        
        if(count == 1) return false;
        for(int i=2; i<count; i++) {
            if(count%i == 0) return false;
        }
        
        return true;
    }
}