Reduce a given Binary Array to a single element by removal of Triplets

Given an binary array arr[] cof size N, the task is to reduce the array to a single element by the following two operations: 
 

  • A triplet of consecutive 0‘s or 1‘s remains unchanged.
  • A triplet of consecutive array elements consisting of two 0’s and a single 1 or vice versa can be converted to more frequent element.

Examples: 
 

Input: arr[] = {0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1} 
Output: No 
Explanation: 
Following are the operations performed on the array: 
{0, 1, 1} -> 1 modifies the array to {1, 1, 1, 0, 0, 1, 1, 1, 1} 
{1, 0, 0} -> 0 modifies the array to {1, 1, 0, 1, 1, 1, 1} 
{1, 0, 1} -> 1 modifies the array to {1, 1, 1, 1, 1} 
Since, all the remaining elements are 1, they remain unchanged. 
Therefore, the array cannot be reduced to a single element.
Input: arr[] = {1, 0, 0, 0, 1, 1, 1} 
Output: Yes 
Explanation: 
Following are the operations performed on the array: 
{1, 0, 0} -> 0 {0, 0, 1, 1, 1} 
{0, 0, 1} -> 0 {0, 1, 1} 
{0, 1, 1} -> 1 {1} 
 

 

Approach: 
Follow the steps below to solve the problem: 
 



  • Count the frequency of 0‘s and 1‘s.
  • Calculate the absolute difference their respective counts.
  • If the difference is 1, only then the array can be reduced to 1. Therefore, print Yes.
  • Otherwise, print No.

Below is the implementation of the above approach:
 

C++

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// C++ program to implement
// the above approach
#include <bits/stdc++.h>
using namespace std;
  
// Function to check if it is possible to
// reduce the array to a single element
void solve(int arr[], int n)
{
    // Stores frequency of 0's
    int countzeroes = 0;
  
    // Stores frequency of 1's
    int countones = 0;
  
    for (int i = 0; i < n; i++) {
  
        if (arr[i] == 0)
            countzeroes++;
        else
            countones++;
    }
  
    // Condition for array to be reduced
    if (abs(countzeroes - countones) == 1)
        cout << "Yes";
  
    // Otherwise
    else
        cout << "No";
}
  
// Driver Code
int main()
{
    int arr[] = { 0, 1, 0, 0, 1, 1, 1 };
  
    int n = sizeof(arr) / sizeof(arr[0]);
  
    solve(arr, n);
  
    return 0;
}

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Java

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// Java program to implement
// the above approach
class GFG{
  
// Function to check if it is possible to
// reduce the array to a single element
static void solve(int arr[], int n)
{
      
    // Stores frequency of 0's
    int countzeroes = 0;
  
    // Stores frequency of 1's
    int countones = 0;
  
    for(int i = 0; i < n; i++) 
    {
        if (arr[i] == 0)
            countzeroes++;
        else
            countones++;
    }
  
    // Condition for array to be reduced
    if (Math.abs(countzeroes - countones) == 1)
        System.out.print("Yes");
  
    // Otherwise
    else
        System.out.print("No");
}
  
// Driver Code
public static void main(String[] args)
{
    int arr[] = { 0, 1, 0, 0, 1, 1, 1 };
  
    int n = arr.length;
  
    solve(arr, n);
}
}
  
// This code is contributed by 29AjayKumar

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Output: 

Yes

 

Time Complexity: O(N) 
Auxiliary Space: O(1)
 

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