A Boolean Array Puzzle

Last Updated : 11 Nov, 2023

Input: A array arr[] of two elements having value 0 and 1
Output: Make both elements 0.

Specifications: Following are the specifications to follow.

1) It is guaranteed that one element is 0 but we do not know its position.
2) We can’t say about another element it can be 0 or 1.
3) We can only complement array elements, no other operation like and, or, multi, division, …. etc.
4) We can’t use if, else and loop constructs.
5) Obviously, we can’t directly assign 0 to array elements.

There are several ways we can do it as we are sure that always one Zero is there. Thanks to devendraiiit for suggesting following 3 methods.

Method 1

C++

#include <bits/stdc++.h> 
using namespace std; 
void changeToZero(int a[2]) 
{ 
    a[ a[1] ] = a[ !a[1] ]; 
} 
 
// Driver code 
int main() 
{ 
    int a[] = {1, 0}; 
    changeToZero(a); 
     
    cout<<"arr[0] = "<<a[0]<<endl; 
    cout<<" arr[1] = "<<a[1]; 
    return 0; 
} 
 
// This code is contributed by rathbhupendra 

C

void changeToZero(int a[2]) 
{ 
a[ a[1] ] = a[ !a[1] ]; 
} 
 
int main() 
{ 
int a[] = {1, 0}; 
changeToZero(a); 
 
printf(" arr[0] = %d \n", a[0]); 
printf(" arr[1] = %d ", a[1]); 
getchar(); 
return 0; 
} 

Java

import java.io.*;
 
class GFG{
 
public static void changeToZero(int a[]) 
{ 
    a[a[1]] = a[1 - a[1]]; 
} 
 
// Driver code
public static void main(String args[])
{ 
    int[] arr;
    arr = new int[2];
    arr[0] = 1;
    arr[1] = 0;
    changeToZero(arr); 
     
    System.out.println("arr[0]= " + arr[0]); 
    System.out.println("arr[1]= " + arr[1]); 
} 
}
 
// This code is contributed by rohitsingh07052

Python3

def changeToZero(a): 
    a[ a[1] ] = a[ not a[1] ] 
    return a 
 
# Driver code 
if __name__=='__main__': 
    a = [1, 0] 
    a = changeToZero(a); 
     
    print(" arr[0] = " + str(a[0])) 
    print(" arr[1] = " + str(a[1])) 
 
# This code is contributed by Yash_R 

C#

using System;
 
class GFG {
 
    public static void changeToZero(int[] a)
    {
        a[a[1]] = a[1 - a[1]];
    }
 
    // Driver code
    public static void Main()
    {
        int[] arr;
        arr = new int[2];
        arr[0] = 1;
        arr[1] = 0;
        changeToZero(arr);
 
        Console.WriteLine("arr[0]= " + arr[0]);
        Console.WriteLine("arr[1]= " + arr[1]);
    }
}
 
// This code is contributed by souravmahato348.

Javascript

<script>
 
function changeToZero(a) 
{ 
    a[a[1]] = a[1 - a[1]]; 
} 
     
// Driver code
let arr;
arr = [];
arr[0] = 1;
arr[1] = 0;
changeToZero(arr); 
 
document.write("arr[0] = " + arr[0] + "<br/>"); 
document.write("arr[1] = " + arr[1]); 
 
// This code is contributed by avijitmondal1998
 
</script>

Time Complexity: O(1)

Auxiliary Space: O(1)

Method 2

C++

void changeToZero(int a[2])
{
    a[ !a[0] ] = a[ !a[1] ];
}

C

void changeToZero(int a[2]) 
{ 
    a[ !a[0] ] = a[ !a[1] ] 
} 

Java

void changeToZero(int [2]a) { 
  a[!a[0]] = a[!a[1]];
}
 
// This code is contributed by souravmahato348.

Python3

def changeToZero(a):
     
    a[ !a[0] ] = a[ !a[1] ]
   
  # This code is contributed by sanjoy_62.

C#

static void changeToZero(int [2]a) { 
  a[!a[0]] = a[!a[1]];
}
 
// This code is contributed by souravmahato348.

Javascript

<script>
function changeToZero(a) 
{ 
    a[ !a[0] ] = a[ !a[1] ];
} 
 
// This code is contributed by souravmahato348.
</script>

Time Complexity: O(1)

Auxiliary Space: O(1)

Method 3
This method doesn’t even need complement.

C++

#include <iostream>
using namespace std;
 
void changeToZero(int a[2]) 
{ 
    a[ a[1] ] = a[ a[0] ] 
} 
 
 
int main() {
 
    cout << "GFG!";
    return 0;
}

C

void changeToZero(int a[2]) 
{ 
    a[ a[1] ] = a[ a[0] ] 
} 

Java

static void changeToZero(int a[2]) 
{ 
    a[ a[1] ] = a[ a[0] ] 
} 
 
// this code is contributed by shivanisinghss2110

Python3

def changeToZero(a) :
     
    a[ a[1] ] = a[ a[0] ]

C#

static void changeToZero(int[] a) 
{ 
    a[ a[1] ] = a[ a[0] ];
}
 
//this code is contributed by phasing17

Javascript

function changeToZero(a) 
{ 
     a[ a[1] ] = a[ a[0] ];
} 
 
 
//this code is contributed by phasing17

Time Complexity: O(1)

Auxiliary Space: O(1)

Method 4
Thanks to purvi for suggesting this method.

C++

#include <iostream>
using namespace std;
 
 
void changeToZero(int a[2])
{
  a[0] = a[a[0]];
  a[1] = a[0];
}
 
 
int main() {
 
    cout << "GFG!";
    return 0;
}

C

void changeToZero(int a[2])
{
  a[0] = a[a[0]];
  a[1] = a[0];
}

Java

static void changeToZero(int a[])
{
  a[0] = a[a[0]];
  a[1] = a[0];
}
//This code is contributed by shruti456rawal

Python3

# Python code for the above approach
 
def changeToZero(a) :
     
    a[0] = a[a[0]]
    a[1] = a[0]
 
    # This code is contributed by splevel62.

C#

static void changeToZero(int[] a)
{
  a[0] = a[a[0]];
  a[1] = a[0];
}
//This code is contributed by shruti456rawal

Javascript

// JavaScript function to implement
// the approach
 
function changeToZero(a)
{
  a[0] = a[a[0]];
  a[1] = a[0];
}
 
// This code is contributed by phasing17

Time Complexity: O(1)

Auxiliary Space: O(1)

There may be many more methods.
Please write comments if you find the above codes incorrect, or find other ways to solve the same problem.

Make Array Equal

kartik

Improve

Article Tags :

Practice Tags :

Bit Magic

A Boolean Array Puzzle

C++

C

Java

Python3

C#

Javascript

C++

C

Java

Python3

C#

Javascript

C++

C

Java

Python3

C#

Javascript

C++

C

Java

Python3

C#

Javascript

Similar Reads

Thank You!

What kind of Experience do you want to share?