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  1. Prepare
  2. Algorithms
  3. Bit Manipulation
  4. 2's complement
  5. Discussions

2's complement

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40 Discussions

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  • jmcparland
     + 0 comments

    Honestly, some puzzles just aren't worth the time / points. This one looks like it's just bookkeeping.

    Running the range and doing pop-counts takes too long. Instead, given the range, determine how often each of the 32-bits possible will be a 1. The range may contain some number of full cycles, with half 1s and half 0s, and then some off-cycle handling on either end. Might have to handle a case for the positive portion of the range and a case for the negatives -- TBD.

  • thecodingsoluti2
     + 0 comments

    Here is 2"s complement problem solution in Python Java C++ and c programming- https://programs.programmingoneonone.com/2021/07/hackerrank-2s-complement-problem-solution.html

  • TChalla
     + 0 comments

    Python3 solution

    # Enter your code here. Read input from STDIN. Print output to STDOUT
def count1s(n,i):
    if i == 1:
        return n & 1
    mask = 1 << i - 1
    remainder = (0xFFFFFFFF >> (32-i+1))&n
    return (n & mask > 0) * ((mask * (i - 1) >> 1) + 1 + remainder) + count1s(remainder, i - 1)

def startCount():
    iterations = int(input())
    lis = []
    while iterations > 0:
        n1, n2 = [int(x) for x in input().split()] 
        lis.append([n1, n2])
        iterations -= 1
    for element in lis:
        if (element[0] > 0) or (element[1] < 0):
            print(count1s(element[1], 32) - count1s(element[0] - 1, 32))
        else:
            print((1 << 36) - count1s(element[0] - 1, 32) + count1s(element[1], 32))

startCount()

  • alfonso_csrz
     + 1 comment

    https://www.youtube.com/watch?v=4qH4unVtJkE If someone is interested

  • i_am_ironman
     + 0 comments

    Can't figure out why it is not working

    import java.io.*;
import java.math.*;
import java.text.*;
import java.util.*;
import java.util.regex.*;
import java.lang.*;

public class Solution 
{
    static int table[] = new int[256];
    static void initialize()
    {
        table[0]=0;
        for (int i = 1 ; i < 256; i++ )
        {
            table[i] = (i&1)+table[i/2];
        }
    }
    static int countBit(int n)
    {
        return table[n & 0xff ] + table[(n>>8) & 0xff ] + table[(n>>16) & 0xff ] + table[(n>>24) & 0xff ];
    }
    static int twosCompliment(int a, int b) 
    {
        int ret = 0;
        if ( a >=0 && b>=0 || a <=0 && b <= 0)
        {
            for (int i = a ; i <= b ;i++)
            {
            ret+= countBit(i);
            }
        }
        else
        {
            int hashMap[] = new int[b-a+1];
            for (int i = a ; i <= b ; i++ )
            {
                // System.out.println(i);
                if (i == 0)
                {
                    ret+=0;
                }
                else if (i < 0)
                {
                    int temp = countBit(i);
                    hashMap[i*-1 -1 ]= temp;
                    ret+=temp;
                }
                else if (i > 0 && hashMap[i] != 0)
                {
                    ret+=countBit(i);
                }
                else if (i > 0 && hashMap[i] ==0 )
                {
                    ret+=countBit(i);
                }
            }
        }
        return ret;
    }

    private static final Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) throws IOException {
        
        int t = Integer.parseInt(scanner.nextLine().trim());
        initialize();
        for (int tItr = 0; tItr < t; tItr++) {
            // String[] ab = scanner.nextLine().split(" ");

            // int a = Integer.parseInt(ab[0].trim());

            // int b = Integer.parseInt(ab[1].trim());
            int a = scanner.nextInt();
            int b = scanner.nextInt();

            // int result =0 ;

            System.out.println(twosCompliment(a, b));
            // bufferedWriter.write(String.valueOf(result));
            // bufferedWriter.newLine();
        }

        // bufferedWriter.close();
    }
}