Create Array by replacing any element with its immediate smaller neighbour

Given an integer array arr[] of size N, the task is to generate a new array by replacing i^th element with its immediate right smaller neighbour i.e., by (i+t)^th element if it is smaller.

Examples:

Input: N = 5, Arr[] = {4, 2, 1, 5, 3}
Output: 2 1 -1 3 -1
Explanation: Array elements are 4, 2, 1, 5, 3.
Next to 4 is 2 which is smaller, so we print 2. Next of 2 is 1 which is smaller, so we print 1. Next of 1 is 5 which is greater, so we print -1. Next of 5 is 3 which is smaller, so we print 3.  Note that for last element, output is always  going to be -1 because there is no element on right.

Input: N = 6, Arr[] = {5, 6, 2, 3, 1, 7}
Output: -1 2 -1 1 -1 -1

Approach: To solve the problem follow the below idea:

The idea is to traverse the array and check if the next element is smaller or not. If next element is smaller then replace current element with next smaller element otherwise replace current element with -1.

Follow the steps below to implement the above idea:

• Iterate over the array i = 0 to i < size of array – 1
  • Check if the current element is greater than the next element, (i.e, arr[i] > arr[i + 1])
    • If true, replace arr[i] = arr[i + 1]
    • Otherwise, replace arr[i] = -1

Below is the implementation of the above approach.

C++

// C++ code to implement the approach

#include <bits/stdc++.h>
using namespace std;

// Function to create the new array
void immediateSmaller(vector<int>& arr, int n)
{
    for (int i = 0; i < n - 1; i++) {
        if (arr[i] > arr[i + 1]) {
            arr[i] = arr[i + 1];
        }
        else
            arr[i] = -1;
    }
    arr[n - 1] = -1;
}

// Driver code
int main()
{
    vector<int> arr = { 5, 6, 2, 3, 1, 7 };
    int N = arr.size();

    // Function Call
    immediateSmaller(arr, N);

    for (auto i : arr)
        cout << i << " ";

    return 0;
}

Java

// Java code to implement the approach
import java.io.*;

class GFG
{

  // Function to create the new array
  public static void immediateSmaller(int arr[], int n)
  {
    for (int i = 0; i < n - 1; i++) {
      if (arr[i] > arr[i + 1]) {
        arr[i] = arr[i + 1];
      }
      else
        arr[i] = -1;
    }
    arr[n - 1] = -1;
  }

  // Driver Code
  public static void main(String[] args)
  {
    int arr[] = { 5, 6, 2, 3, 1, 7 };
    int N = arr.length;

    // Function Call
    immediateSmaller(arr, N);

    for (int i : arr)
      System.out.print(i + " ");
  }
}

// This code is contributed by Rohit Pradhan

Python3

# Python3 code to implement the approach

# Function to create the new array
def immediateSmaller(arr, n) :

    for i in range(n - 1) :
        if (arr[i] > arr[i + 1]) :
            arr[i] = arr[i + 1];

        else :
            arr[i] = -1;

    arr[n - 1] = -1;

# Driver code
if __name__ == "__main__" :

    arr = [ 5, 6, 2, 3, 1, 7 ];
    N = len(arr);

    # Function Call
    immediateSmaller(arr, N);

    for i in arr:
        print(i, end = " ");

   # This code is contributed by AnkThon

C#

// C# code to implement the approach
using System;

class GFG {

  // Function to create the new array
  static void immediateSmaller(int[] arr, int n)
  {
    for (int i = 0; i < n - 1; i++) {
      if (arr[i] > arr[i + 1]) {
        arr[i] = arr[i + 1];
      }
      else
        arr[i] = -1;
    }
    arr[n - 1] = -1;
  }

  // Driver Code
  public static void Main()
  {
    int[] arr = { 5, 6, 2, 3, 1, 7 };
    int N = arr.Length;

    // Function Call
    immediateSmaller(arr, N);

    for (int i = 0; i < arr.Length; i++)
      Console.Write(arr[i] + " ");
  }
}

// This code is contributed by Samim Hossain Mondal.

Javascript

// JavaScript code to implement the approach

// Function to create the new array
function immediateSmaller(arr, n)
{
    for (let i = 0; i < n - 1; i++) {
        if (arr[i] > arr[i + 1]) {
            arr[i] = arr[i + 1];
        }
        else
            arr[i] = -1;
    }
    arr[n - 1] = -1;

    return arr;
}

// Driver code
arr = [ 5, 6, 2, 3, 1, 7 ];
N = arr.length;

// Function Call
rslt = immediateSmaller(arr, N);
let string = "";
for (let i = 0; i < rslt.length ; i++)
    string += rslt[i] + " ";

console.log(string);

// This code is contributed by AnkThon

Output

-1 2 -1 1 -1 -1 

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