30. Count Set Bits in an Integer

#include <stdio.h>
#include <stdint.h>

uint8_t lut_num_bits[] = {0,1,1,2,1,2,2,3,1,2,2,2,2,3,3,4};

int countSetBits(unsigned int n) {
    // Write your code here
    int count = 0;

    unsigned int num = n;
    while(num){
        count += lut_num_bits[num&0xF];
        num >>= 4;
    }
    return count;
}

int main() {
    int n;
    scanf("%d", &n);
    printf("%d", countSetBits(n));
    return 0;
}