BINFUN (July Lunchtime'20)

package Codechef;
import java.io.*;
import java.util.*;
public class BINFUN {
    public static int count(int nums) {
        return 1 + Integer.bitCount(Integer.highestOneBit(nums) - 1);
    }
    public static long value(int nums1, int nums2, int len1, int len2) {
        long x = (nums1<<len2) + nums2;
        long y = (nums2<<len1) + nums1;
        return Math.abs(x-y);
    }
    public static void main(String[] args) throws IOException
    {
        StdIn scn = new StdIn();
        int t = scn.nextInt();
        while (t--> 0) {
            int n = scn.nextInt();
            ArrayList<ArrayList<Integer>> adj = new ArrayList<ArrayList<Integer>>();
            for (int i = 0; i<33; i++) {
                adj.add(new ArrayList<Integer>());
            }
            for (int i = 0; i<n; i++) {
                int nums = scn.nextInt();
                int pos = count(nums);
                adj.get(pos).add(nums);
            }
            for (int i = 0; i<adj.size(); i++) {
                Collections.sort(adj.get(i));
            }
            long ans = -1;
            for (int i = 1; i<32; i++) {
                for (int j = 1; j<32; j++) {
                    if (adj.get(i).isEmpty() || adj.get(j).isEmpty()) continue;
                    ans = Math.max(ans, value(adj.get(i).get(0), adj.get(j).get(adj.get(j).size()-1), i, j));
                }
            }
            System.out.println(ans);
        }
    }
    interface Input {
        public String next();
        public String nextLine();
        public int nextInt();
        public long nextLong();
        public double nextDouble();
    }
    static class StdIn implements Input {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public StdIn() {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public StdIn(String filename) {
            try{
                din = new DataInputStream(new FileInputStream(filename));
            } catch(Exception e) {
                throw new RuntimeException();
            }
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String next() {
            int c;
            while((c=read())!=-1&&(c==' '||c=='\n'||c=='\r'));
            StringBuilder s = new StringBuilder();
            while (c != -1)
            {
                if (c == ' ' || c == '\n'||c=='\r')
                    break;
                s.append((char)c);
                c=read();
            }
            return s.toString();
        }

        public String nextLine() {
            int c;
            while((c=read())!=-1&&(c==' '||c=='\n'||c=='\r'));
            StringBuilder s = new StringBuilder();
            while (c != -1)
            {
                if (c == '\n'||c=='\r')
                    break;
                s.append((char)c);
                c = read();
            }
            return s.toString();
        }

        public int nextInt() {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            }  while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public int[] readIntArray(int n) {
            int[] ar = new int[n];
            for(int i=0; i<n; ++i)
                ar[i]=nextInt();
            return ar;
        }

        public long nextLong() {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public long[] readLongArray(int n) {
            long[] ar = new long[n];
            for(int i=0; i<n; ++i)
                ar[i]=nextLong();
            return ar;
        }

        public double nextDouble() {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() {
            try{
                if (bufferPointer == bytesRead)
                    fillBuffer();
                return buffer[bufferPointer++];
            } catch(IOException e) {
                throw new RuntimeException();
            }
        }

        public void close() throws IOException {
            if (din == null)
                return;
            din.close();
        }
    }
 }