A Boolean Array Puzzle - GeeksforGeeks

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; 
} 

Python3

# Python3 program for a  
# boolean array puzzle 
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 

Method 2

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

Method 3
This method doesn’t even need complement.

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

Method 4
Thanks to purvi for suggesting this method.

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

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.

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My Personal Notes

C++

C

Python3

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