Represent a number N in base -2

Last Updated : 23 Jul, 2021

Given an integer N, the task is to find base -2 representation of the number N in the form of a string, such that S₀* (- 2)⁰ + S₁* (- 2)¹ + … + S_k* (- 2)^k = N. The string should only consist of 0s and 1s and unless the string is equal to zero, the initial character should be 1.

Examples:

Input: N = -9
Output: 1011
Explanation: 1011 is -2 representation of -9
(-2)⁰+ (-2)¹+ (-2)³ = 1+ (-2) + (-8) = -9

Input: N = -7
Output: 1001

Approach: Follow the steps below to solve the problem:

Initialize an empty string S.
Iterate from N, until N is greater than zero.
- If N is even, append ‘0‘ in front of S and divide N by -2.
- Otherwise, append ‘1‘ in front of S, and decrement N by 1, and then divide N by -2.
If the string S is empty, then return ‘0‘
Finally, return the string S.

Below is the implementation of the above approach:

C++

// C++ Program for above approach
#include <bits/stdc++.h>
using namespace std;
 
// Function to convert N to
// equivalent representation in base -2
string BaseConversion(int N)
{
 
    // Stores the required answer
    string s = "";
 
    // Iterate until N is
    // not equal to zero
    while (N != 0) {
 
        // If N is Even
        if (N % 2 == 0) {
 
            // Add char '0' in
            // front of string
            s = "0" + s;
        }
        else {
 
            // Add char '1' in
            // front of string
            s = "1" + s;
 
            // Decrement N by 1
            N--;
        }
 
        // Divide N by -2
        N /= -2;
    }
 
    // If string is empty,
    // that means N is zero
    if (s == "") {
 
        // Put '0' in string s
        s = "0";
    }
    return s;
}
 
// Driver Code
int main()
{
 
    // Given Input
    int N = -9;
 
    // Function Call
    cout << BaseConversion(N);
    return 0;
}

Java

// Java Program for above approach
class GFG {
    // Function to convert N to
    // equivalent representation in base -2
    public static String BaseConversion(int N) {
 
        // Stores the required answer
        String s = "";
 
        // Iterate until N is
        // not equal to zero
        while (N != 0) {
 
            // If N is Even
            if (N % 2 == 0) {
 
                // Add char '0' in
                // front of string
                s = "0" + s;
            } else {
 
                // Add char '1' in
                // front of string
                s = "1" + s;
 
                // Decrement N by 1
                N--;
            }
 
            // Divide N by -2
            N /= -2;
        }
 
        // If string is empty,
        // that means N is zero
        if (s == "") {
 
            // Put '0' in string s
            s = "0";
        }
        return s;
    }
 
    // Driver Code
    public static void main(String args[]) {
 
        // Given Input
        int N = -9;
 
        // Function Call
        System.out.println(BaseConversion(N));
    }
 
}
 
// This code is contributed by _saurabh_jaiswal.

Python3

# Python Program for the above approach
 
# Function to convert N to
# equivalent representation in base -2
def BaseConversion(N):
 
    # Stores the required answer
    s = ""
 
    # Iterate until N is
    # not equal to zero
    while (N != 0):
 
        # If N is Even
        if (N % 2 == 0):
 
            # Add char '0' in
            # front of string
            s = "0" + s
 
        else:
 
            # Add char '1' in
            # front of string
            s = "1" + s
 
            # Decrement N by 1
            N -= 1
 
        # Divide N by -2
        N /= -2
 
    # If string is empty,
    # that means N is zero
    if (s == ""):
 
        # Put '0' in string s
        s = "0"
 
    return s
 
 
# Driver Code
 
# Given Input
N = -9
 
# Function Call
print(BaseConversion(N))
 
# This code is contributed by _saurabh_jaiswal

C#

// C# Program for above approach
using System;
using System.Collections.Generic;
 
class GFG{
 
// Function to convert N to
// equivalent representation in base -2
static string BaseConversion(int N)
{
 
    // Stores the required answer
    string s = "";
 
    // Iterate until N is
    // not equal to zero
    while (N != 0) {
 
        // If N is Even
        if (N % 2 == 0) {
 
            // Add char '0' in
            // front of string
            s = "0" + s;
        }
        else {
 
            // Add char '1' in
            // front of string
            s = "1" + s;
 
            // Decrement N by 1
            N--;
        }
 
        // Divide N by -2
        N /= -2;
    }
 
    // If string is empty,
    // that means N is zero
    if (s == "") {
 
        // Put '0' in string s
        s = "0";
    }
    return s;
}
 
// Driver Code
public static void Main()
{
 
    // Given Input
    int N = -9;
 
    // Function Call
    Console.Write(BaseConversion(N));
}
}
 
// This code is contributed by bgangwar59.

Javascript

<script>
       // JavaScript Program for the above approach
 
       // Function to convert N to
       // equivalent representation in base -2
       function BaseConversion(N)
       {
 
           // Stores the required answer
           let s = "";
 
           // Iterate until N is
           // not equal to zero
           while (N != 0) {
 
               // If N is Even
               if (N % 2 == 0) {
 
                   // Add char '0' in
                   // front of string
                   s = "0" + s;
               }
               else {
 
                   // Add char '1' in
                   // front of string
                   s = "1" + s;
 
                   // Decrement N by 1
                   N--;
               }
 
               // Divide N by -2
               N /= -2;
           }
 
           // If string is empty,
           // that means N is zero
           if (s == "") {
 
               // Put '0' in string s
               s = "0";
           }
           return s;
       }
 
       // Driver Code
 
 
       // Given Input
       let N = -9;
 
       // Function Call
       document.write(BaseConversion(N));
 
   // This code is contributed by Potta Lokesh
   </script>