2. 코드

public class NextBigNumber {
    private int nextBigNumber(int n) {
        int count = bitCount(n);
        while ( true ) {
            n++;
            if ( count == bitCount(n) )
                break;
        }
        return n;
    }
 
    private int bitCount(int n) {
        String binNum = Integer.toBinaryString(n);
        int count = 0;
        for ( int inx=0; inx<binNum.length(); inx++ ) {
            char c = binNum.charAt(inx);
            if ( c == '1' ) {
                count++;
            }
        }
        return count;
    }
 
    public static void main(String[] args) {
        NextBigNumber nbn = new NextBigNumber();
        int n = 78;
        System.out.println(nbn.nextBigNumber(n));
    }
}