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Replace the middle element of the longest subarray of 0s from the right exactly K times

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  • Difficulty Level : Easy
  • Last Updated : 27 Dec, 2022
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Given an array arr[] of size N, consisting of 0s initially, and a positive integer K, the task is to print the array elements by performing the following operations exactly K times.

  • For every ith operation select the rightmost longest subarray consisting of all 0s and replace the mid element of the subarray by i.
  • If two middle elements exist, then check if i is an even number or not. If found to be true, then replace the rightmost middle element with i.
  • Otherwise, replace the leftmost middle element with i.
    • Initialize a Priority Queue, say pq, to store the subarrays of the form { X, Y} where X denotes the length of the subarray and Y denotes the starting index of the subarray.
    • Initially maximum length of the subarray with all 0s is N and start index of the subarray is 0. Therefore, Insert { N, 0 } into pq.
    • Iterate over the range [1, K] using variable i. For every ith operation pop the top element from pq and check if length of the popped element is an odd number or not. If found to be true then replace the mid element of the subarray with i.
    • Otherwise, if i is an even number then replace the rightmost mid element of the subarray with i. Otherwise, replace the leftmost mid element of the subarray with i.
    • After replacing the mid element with i, insert the left half of the subarray and right half of the subarray containing all 0s into pq.
    • Finally, print the array elements.

Below is the implementation of the above approach:

C++




// C++ program to implement
// the above approach
 
 
#include <bits/stdc++.h>
using namespace std;
 
 
 
// Function to print array by replacing the mid
// of the righmost longest subarray with count
// of operations performed on the array
void ReplaceArray(int arr[], int N, int K)
{
     
     
    // Stores subarray of the form { X, Y },
    // where X is the length and Y is start
    // index of the subarray
    priority_queue<vector<int> > pq;
     
     
     
    // Insert the array arr[]
    pq.push({ N, 0 });
     
     
     
    // Stores index of mid
    // element of the subarray
    int mid;
     
     
     
    // Iterate over the range [1, N]
    for (int i = 1; i <= K; i++) {
         
         
         
        // Stores top element of pq
        vector<int> sub = pq.top();
         
         
         
        // Pop top element of pq
        pq.pop();
         
         
         
        // If length of the subarray
        // is an odd number
        if (sub[0] % 2 == 1) {
             
             
             
            // Update mid
            mid = sub[1] + sub[0] / 2;
             
             
             
            // Replacing arr[mid] with i
            arr[mid] = i;
             
             
             
            // Insert left half of
            // the subarray into pq
            pq.push({ sub[0] / 2,
                        sub[1] });
             
             
             
            // Insert right half of
            // the subarray into pq
            pq.push({ sub[0] / 2,
                        (mid + 1) });
        }
         
         
         
        // If length of the current
        // subarray is an even number
        else {
             
             
             
            // If i is
            // an odd number
            if (i % 2 == 1) {
                 
                 
                 
                // Update mid
                mid = sub[1] + sub[0] / 2;
                 
                 
                 
                // Replacing mid element
                // with i
                arr[mid - 1] = i;
                 
                 
                 
                // Insert left half of
                // the subarray into pq
                pq.push({ sub[0] / 2 - 1,
                            sub[1] });
                 
                 
                 
                // Insert right half of
                // the subarray into pq
                pq.push({ sub[0] / 2, mid });
            }
             
             
             
            // If i is an even number
            else {
                 
                 
                 
                // Update mid
                mid = sub[1] + sub[0] / 2;
                 
                 
                 
                // Replacing mid element
                // with i
                arr[mid - 1] = i;
                 
                 
                 
                // Insert left half of
                // the subarray into pq
                pq.push({ sub[0] / 2,
                            sub[1] });
                 
                 
                 
                // Insert right half of
                // the subarray into pq
                pq.push({ sub[0] / 2 - 1,
                        (mid + 1) });
            }
        }
    }
     
     
     
    // Print array elements
    for (int i = 0; i < N; i++)
        cout << arr[i] << " ";
}
 
 
// Driver Code
int main()
{
     
    int arr[] = { 0, 0, 0, 0, 0 };
    int N = sizeof(arr) / sizeof(arr[0]);
    int K = 3;
    ReplaceArray(arr, N, K);
}

Java




import java.util.*;
 
class Tuple
{
  public int x, y;
  public Tuple(int a, int b)
  {
    x = a;
    y = b;
  }
}
 
class GFG {
 
 
  // Function to print array by replacing the mid
  // of the righmost longest subarray with count
  // of operations performed on the array
  static void replaceArray(int[] arr, int N, int K) {
 
    // Stores subarray of the form { X, Y },
    // where X is the length and Y is start
    // index of the subarray
    List<Tuple> pq = new ArrayList<>();
 
    // Insert the array arr[]
    pq.add(new Tuple(N, 0));
 
    // Stores index of mid
    // element of the subarray
    int mid;
 
    // Iterate over the range [1, N]
    for (int i = 1; i <= K; i++) {
 
      // Stores top element of pq
      Tuple sub = pq.get(0);
 
      // Pop top element of pq
      pq.remove(0);
 
      // If length of the subarray
      // is an odd number
      if (sub.x % 2 == 1) {
 
        // Update mid
        mid = sub.y + sub.x / 2;
 
        // Replacing arr[mid] with i
        arr[mid] = i;
 
        // Insert left half of
        // the subarray into pq
        pq.add(new Tuple(sub.x / 2, sub.y));
 
        // Insert right half of
        // the subarray into pq
        pq.add(new Tuple(sub.x / 2, (mid + 1)));
      }
 
      // If length of the current
      // subarray is an even number
      else {               
 
        // If i is
        // an odd number
        if (i % 2 == 1) {
 
          // Update mid
          mid = sub.y + sub.x / 2;
 
          // Replacing mid element
          // with i
          arr[mid - 1] = i;
 
          // Insert left half of
          // the subarray into pq
          pq.add(new Tuple(sub.x / 2 - 1, sub.y));
 
          // Insert right half of
          // the subarray into pq
          pq.add(new Tuple(sub.x / 2, mid));
        }               
 
        // If i is an even number
        else {
 
          // Update mid
          mid = sub.y + sub.x / 2;
 
          // Replacing mid element
          // with i
          arr[mid - 1] = i;
 
          // Insert left half of
          // the subarray into pq
          pq.add(new Tuple(sub.x / 2, sub.y));
 
          // Insert right half of
          // the subarray into pq
          pq.add(new Tuple(sub.x / 2 - 1, (mid + 1)));
        }
      }
 
      pq.sort((a, b) -> (a.x != b.x) ?
              - a.x + b.x :
              - a.y + b.y);
    }
 
 
    // Print array elements
    for (int i = 0; i < N; i++)
      System.out.print( arr[i] + " ");
  }
 
  // Driver Code
  public static void main(String[] args)
  {
 
    int[] arr = { 0, 0, 0, 0, 0 };
    int N = arr.length;
    int K = 3;
    replaceArray(arr, N, K);
  }
}
 
// This code is contributed by phasing17.

Python3




# Python3 program to implement
# the above approach
 
# Function to print array by replacing the mid
# of the righmost longest subarray with count
# of operations performed on the array
def ReplaceArray(arr, N, K):
 
    # Stores subarray of the form  X, Y ,
    # where X is the length and Y is start
    # index of the subarray
    pq = [];
     
    # Insert the array arr[]
    pq.append([ N, 0 ]);
     
    # Stores index of mid
    # element of the subarray
    mid = 0
     
    # Iterate over the range [1, N]
    for i in range(1, 1 + N):
         
        # Stores top element of pq
        sub = pq[-1]
         
        # Pop top element of pq
        pq.pop();
         
        # If length of the subarray
        # is an odd number
        if (sub[0] % 2 == 1) :
                 
            # Update mid
            mid = int(sub[1] + int(sub[0] / 2));
             
            # Replacing arr[mid] with i
            arr[mid] = i;
                 
            # Insert left half of
            # the subarray into pq
            pq.append([ int(sub[0] / 2),  sub[1] ]);
                 
            # Insert right half of
            # the subarray into pq
            pq.append([ int(sub[0] / 2), (mid + 1) ]);
         
         
        # If length of the current
        # subarray is an even number
        else :
                 
            # If i is
            # an odd number
            if (i % 2 == 1) :
                         
                # Update mid
                mid = sub[1] + int(sub[0] / 2);
                         
                # Replacing mid element
                # with i
                arr[mid - 1] = i;
                 
                # Insert left half of
                # the subarray into pq
                pq.append([ int(sub[0] / 2) - 1, sub[1] ]);
                 
                         
                # Insert right half of
                # the subarray into pq
                pq.append([ int(sub[0] / 2), mid ]);
             
                     
            # If i is an even number
            else :
                             
                # Update mid
                mid = sub[1] + int(sub[0] / 2);
                             
                # Replacing mid element
                # with i
                arr[mid - 1] = i;
                             
                # Insert left half of
                # the subarray into pq
                pq.append([ int(sub[0] / 2),  sub[1] ]);
                             
                # Insert right half of
                # the subarray into pq
                pq.append([ int(sub[0] / 2) - 1, (mid + 1) ]);
                 
            pq.sort()
     
    # Print array elements
    print(*arr)
 
# Driver Code
arr = [ 0, 0, 0, 0, 0 ];
N = len(arr)
K = 3
ReplaceArray(arr, N, K);
 
# This code is contributed by phasing17.

C#




// C# program to implement
// the above approach
using System;
using System.Linq;
using System.Collections.Generic;
 
class GFG
{
   
    // Function to print array by replacing the mid
    // of the righmost longest subarray with count
    // of operations performed on the array
    static void ReplaceArray(int[] arr, int N, int K)
    {
            
        // Stores subarray of the form { X, Y },
        // where X is the length and Y is start
        // index of the subarray
        var pq = new List<Tuple<int, int>>();
      
        // Insert the array arr[]
        pq.Add(Tuple.Create(N, 0));
                 
        // Stores index of mid
        // element of the subarray
        int mid;
                
        // Iterate over the range [1, N]
        for (int i = 1; i <= K; i++)
        {
                        
            // Stores top element of pq
            var sub = pq[0];
             
            // Pop top element of pq
            pq.RemoveAt(0);
             
            // If length of the subarray
            // is an odd number
            if (sub.Item1 % 2 == 1) {
                        
                // Update mid
                mid = sub.Item2 + sub.Item1 / 2;
                        
                // Replacing arr[mid] with i
                arr[mid] = i;
                    
                // Insert left half of
                // the subarray into pq
                pq.Add(Tuple.Create(sub.Item1 / 2,
                            sub.Item2));
                         
                // Insert right half of
                // the subarray into pq
                pq.Add(Tuple.Create(sub.Item1 / 2,
                            (mid + 1)));
            }
              
            // If length of the current
            // subarray is an even number
            else {               
                 
                // If i is
                // an odd number
                if (i % 2 == 1) {
                                    
                    // Update mid
                    mid = sub.Item2 + sub.Item1 / 2;
                                      
                    // Replacing mid element
                    // with i
                    arr[mid - 1] = i;
                                 
                    // Insert left half of
                    // the subarray into pq
                    pq.Add(Tuple.Create(sub.Item1 / 2 - 1,
                                sub.Item2));
                                    
                    // Insert right half of
                    // the subarray into pq
                    pq.Add(Tuple.Create(sub.Item1 / 2, mid));
                }               
                 
                // If i is an even number
                else {
                                      
                    // Update mid
                    mid = sub.Item2 + sub.Item1 / 2;
                                  
                    // Replacing mid element
                    // with i
                    arr[mid - 1] = i;
                                     
                    // Insert left half of
                    // the subarray into pq
                    pq.Add(Tuple.Create(sub.Item1 / 2,
                                sub.Item2));
                                    
                    // Insert right half of
                    // the subarray into pq
                    pq.Add(Tuple.Create(sub.Item1 / 2 - 1,
                            (mid + 1)));
                }
            }
             
            pq = pq.OrderBy(p => -p.Item1).ThenBy(p => -p.Item2).ToList();
        }
         
        // Print array elements
        for (int i = 0; i < N; i++)
            Console.Write( arr[i] + " ");
    }
      
    // Driver Code
    public static void Main(string[] args)
    {
         
        int[] arr = { 0, 0, 0, 0, 0 };
        int N = arr.Length;
        int K = 3;
        ReplaceArray(arr, N, K);
    }
}

Javascript




// JS program to implement
// the above approach
 
// Function to print array by replacing the mid
// of the righmost longest subarray with count
// of operations performed on the array
function ReplaceArray(arr, N, K)
{
 
    // Stores subarray of the form { X, Y },
    // where X is the length and Y is start
    // index of the subarray
    let pq = [];
     
    // Insert the array arr[]
    pq.push([ N, 0 ]);
     
    // Stores index of mid
    // element of the subarray
    let mid;
     
    // Iterate over the range [1, N]
    for (let i = 1; i <= K; i++) {
         
        // Stores top element of pq
        let sub = pq[pq.length - 1]
         
        // Pop top element of pq
        pq.pop();
         
        // If length of the subarray
        // is an odd number
        if (sub[0] % 2 == 1) {
                 
            // Update mid
            mid = Math.floor(sub[1] + Math.floor(sub[0] / 2));
             
            // Replacing arr[mid] with i
            arr[mid] = i;
                 
            // Insert left half of
            // the subarray into pq
            pq.push([ Math.floor(sub[0] / 2),
                        sub[1] ]);
                 
            // Insert right half of
            // the subarray into pq
            pq.push([ Math.floor(sub[0] / 2),
                        (mid + 1) ]);
        }
         
        // If length of the current
        // subarray is an even number
        else {
                 
            // If i is
            // an odd number
            if (i % 2 == 1) {
                         
                // Update mid
                mid = sub[1] + Math.floor(sub[0] / 2);
                         
                // Replacing mid element
                // with i
                arr[mid - 1] = i;
                 
                // Insert left half of
                // the subarray into pq
                pq.push([ Math.floor(sub[0] / 2) - 1,
                            sub[1] ]);
                 
                         
                // Insert right half of
                // the subarray into pq
                pq.push([ Math.floor(sub[0] / 2), mid ]);
            }
                     
            // If i is an even number
            else {
                             
                // Update mid
                mid = sub[1] + Math.floor(sub[0] / 2);
                             
                // Replacing mid element
                // with i
                arr[mid - 1] = i;
                             
                // Insert left half of
                // the subarray into pq
                pq.push([ Math.floor(sub[0] / 2),
                            sub[1] ]);
                             
                // Insert right half of
                // the subarray into pq
                pq.push([ Math.floor(sub[0] / 2) - 1,
                        (mid + 1) ]);
            }
        }
        pq.sort()
    }
     
    // Print array elements
    console.log(arr.join(" "))
 
}
 
// Driver Code
let arr = [ 0, 0, 0, 0, 0 ];
let N = arr.length
let K = 3
ReplaceArray(arr, N, K);
 
// This code is contributed by phasing17.

Output

3 0 1 2 0 

Time Complexity: O(K * log(N))
Auxiliary Space: O(N)


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