Leetcode 762. Prime Number of Set Bits in Binary Representation

 

思路：动态规划。注意1024*1024>10^6，所以质素范围是(0,23)。

class Solution {
    public int countPrimeSetBits(int L, int R) {
        Set<Integer> prime = new HashSet<Integer>(Arrays.asList(2,3,5,7,11,13,17,19,23));
        int[] count = new int[1+R];
        int res = 0;
        for(int i = 1; i <=R; i++) count[i] = count[i>>1] + (i&1);
        for(int i = L; i <=R; i++) {
            if(prime.contains(count[i])) res++;
        }
        return res;
    }
}