Replace every element with the smallest of all other array elements

Given an array arr[] which consist of N integers, the task is to replace every element by the smallest of all other elements present in the array. 

Examples: 

Input: arr[] = {1, 1, 1, 2} 
Output: 1 1 1 1

Input: arr[] = {4, 2, 1, 3} 
Output: 1 1 2 1  

Naive Approach: 
The simplest approach is to find the smallest of all remaining elements for every element with the help of a nested loop.



Time Complexity: O(N2)

Efficient Approach: 
The idea is to maintain prefix and suffix min arrays. Maintain leftMin[] and rightMin[] arrays which stores the minimum on the left and right subarrays for every array element. Once computed, replace every ith index of the original array by storing the minimum of leftMin[i] and rightMin[i].

Below is the implementation of above approach: 

C++

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// C++ program to replace every element
// with the smallest of all other
// array elements
#include<bits/stdc++.h>
using namespace std;
 
void ReplaceElements(int arr[], int n)
{
     
    // There should be atleast two elements
    if (n < 2)
    {
        cout << (" Invalid Input ");
        return;
    }
 
    // leftMin array stores minimum
    // element of left subarray
    int leftMin[n];
    leftMin[0] = INT_MAX;
 
    // rightMin array stores minimum
    // element of right subarray
    int rightMin[n];
    rightMin[n - 1] = INT_MAX;
 
    for(int i = 1; i < n; i++)
    {
       leftMin[i] = min(leftMin[i - 1], arr[i - 1]);
       rightMin[n - 1 - i] = min(rightMin[n - 1 - i + 1],
                                      arr[n - 1 - i + 1]);
    }
     
    // Update original array with minimum
    // of leftMin[i] and rightMin[i]
    for(int i = 0; i < n; i++)
    {
       arr[i] = min(leftMin[i], rightMin[i]);
    }
 
    // Print the modified array.
    for(int i = 0; i < n; ++i)
    {
       cout << arr[i] << " ";
    }
}
 
// Driver code
int main()
{
    int arr[] = { 1, 2, 3, 2 };
     
    int n = sizeof(arr) / sizeof(arr[0]);
 
    ReplaceElements(arr, n);
}
 
// This code is contributed by chitranayal

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Java

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// Java program to replace every element
// with the smallest of all other
// array elements
import java.util.*;
 
class GFG {
 
    static void ReplaceElements(int[] arr, int n)
    {
 
        /* There should be atleast two elements */
        if (n < 2) {
            System.out.println(" Invalid Input ");
            return;
        }
 
        // leftMin array stores minimum
        // element of left subarray
        int[] leftMin = new int[n];
        leftMin[0] = Integer.MAX_VALUE;
 
        // rightMin array stores minimum
        // element of right subarray
        int[] rightMin = new int[n];
        rightMin[n - 1] = Integer.MAX_VALUE;
 
        for (int i = 1; i < n; i++) {
            leftMin[i] = Math.min(leftMin[i - 1],
                                  arr[i - 1]);
            rightMin[n - 1 - i] = Math.min(
                rightMin[n - 1 - i + 1],
                arr[n - 1 - i + 1]);
        }
 
        // Update original array with minimum
        // of leftMin[i] and rightMin[i]
        for (int i = 0; i < n; i++) {
            arr[i] = Math.min(leftMin[i],
                              rightMin[i]);
        }
 
        // Print the modified array.
        for (int i = 0; i < n; ++i) {
            System.out.print(arr[i] + " ");
        }
    }
 
    // Driver code
    public static void main(String[] args)
    {
        int arr[] = { 1, 2, 3, 2 };
        int n = arr.length;
 
        ReplaceElements(arr, n);
    }
}

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Python3

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# Python3 program to replace every
# element with the smallest of all
# other array elements
import sys
 
def ReplaceElements(arr, n):
 
    # There should be atleast two elements
    if (n < 2):
        print(" Invalid Input ")
        return
 
    # leftMin array stores minimum
    # element of left subarray
    leftMin = [0] * n
    leftMin[0] = sys.maxsize
 
    # rightMin array stores minimum
    # element of right subarray
    rightMin = [0] * n
    rightMin[n - 1] = sys.maxsize
 
    for i in range(1, n):
        leftMin[i] = min(leftMin[i - 1],
                             arr[i - 1])
        rightMin[n - 1 - i] = min(rightMin[n - 1 -
                                           i + 1],
                                       arr[n - 1 -
                                           i + 1])
 
    # Update original array with minimum
    # of leftMin[i] and rightMin[i]
    for i in range(n):
        arr[i] = min(leftMin[i],
                    rightMin[i])
 
    # Print the modified array.
    print(*arr, sep = " ")
 
# Driver code
arr = [ 1, 2, 3, 2 ]
n = len(arr)
 
ReplaceElements(arr, n)
 
# This code is contributed by avanitrachhadiya2155

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C#

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// C# program to replace every element
// with the smallest of all other
// array elements
using System;
class GFG{
 
static void ReplaceElements(int[] arr, int n)
{
     
    // There should be atleast two elements
    if (n < 2)
    {
        Console.Write(" Invalid Input ");
        return;
    }
 
    // leftMin array stores minimum
    // element of left subarray
    int[] leftMin = new int[n];
    leftMin[0] = Int32.MaxValue;
 
    // rightMin array stores minimum
    // element of right subarray
    int[] rightMin = new int[n];
    rightMin[n - 1] = Int32.MaxValue;
 
    for(int i = 1; i < n; i++)
    {
       leftMin[i] = Math.Min(leftMin[i - 1],
                                 arr[i - 1]);
       rightMin[n - 1 - i] = Math.Min(
       rightMin[n - 1 - i + 1],
            arr[n - 1 - i + 1]);
    }
 
    // Update original array with minimum
    // of leftMin[i] and rightMin[i]
    for(int i = 0; i < n; i++)
    {
       arr[i] = Math.Min(leftMin[i],
                         rightMin[i]);
    }
 
    // Print the modified array.
    for(int i = 0; i < n; ++i)
    {
       Console.Write(arr[i] + " ");
    }
}
 
// Driver code
public static void Main()
{
    int []arr = { 1, 2, 3, 2 };
    int n = arr.Length;
 
    ReplaceElements(arr, n);
}
}
 
// This code is contributed by Code_Mech

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Output: 

2 1 1 1






 

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

Another Efficient Approach: The idea is to find the smallest and second smallest element in the array by traversing it. Then, traverse the array one more time: 

  • If the current element is the smallest element, then replace it with second smallest element.
  • Else replace the current element with the smallest element

Below is the implementation of the above approach:

C++

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// C++ program to replace every
// element with the smallest
// of all other array elements
#include <bits/stdc++.h>
using namespace std;
 
void ReplaceElements(int arr[], int n)
{
  
    // There should be
    // atleast two elements
    if (n < 2)
    {
        cout << " Invalid Input ";
        return;
    }
  
    // first stores minimum
    // element of the array
    int first = INT_MAX;
  
    // second stores second
    // minimum element of the array
    int second = INT_MAX;
  
    // Find the smallest and second
    // smallest elements of the array
    for(int i = 0; i < n; i++)
    {
          
       // If current element is smaller
       // than first then update both
       // first and second
       if (arr[i] < first)
       {
           second = first;
           first = arr[i];
       }
         
       // If arr[i] is in between
       // first and second
       // then update second
       else if (arr[i] < second &&
                arr[i] != first)
           second = arr[i];
    }
  
    // Update original array with
    // first and second
    for(int i = 0; i < n; i++)
    {
       arr[i] = (arr[i] == first) ?
                  second : first;
    }
  
    // Print the modified array.
    for(int i = 0; i < n; ++i)
    {
       cout << arr[i] << " ";
    }
}
  
// Driver code
int main()
{
    int arr[] = { 1, 2, 3, 2 };
    int n = sizeof(arr) / sizeof(arr[0]);
  
    ReplaceElements(arr, n);
}
  
// This code is contributed by himanshu77

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Java

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// Java program to replace
// every element with the smallest
// of all other array elements
 
import java.util.*;
 
class GFG {
 
    static void ReplaceElements(int[] arr, int n)
    {
 
        // There should be
        // atleast two elements
        if (n < 2) {
            System.out.println(
                " Invalid Input ");
            return;
        }
 
        // first stores minimum
        // element of the array
        int first = Integer.MAX_VALUE;
 
        // second stores second
        // minimum element of the array
        int second = Integer.MAX_VALUE;
 
        // Find the smallest and second
        // smallest elements of the array
        for (int i = 0; i < n; i++) {
 
            // If current element
            // is smaller than first
            // then update both
            // first and second
            if (arr[i] < first) {
                second = first;
                first = arr[i];
            }
 
            // If arr[i] is in between
            // first and second
            // then update second
            else if (arr[i] < second
                     && arr[i] != first)
                second = arr[i];
        }
 
        // Update original array with
        // first and second
        for (int i = 0; i < n; i++) {
 
            arr[i] = (arr[i] == first)
                         ? second
                         : first;
        }
 
        // Print the modified array.
        for (int i = 0; i < n; ++i) {
            System.out.print(arr[i] + " ");
        }
    }
 
    // Driver code
    public static void main(String[] args)
    {
        int arr[] = { 1, 2, 3, 2 };
        int n = arr.length;
 
        ReplaceElements(arr, n);
    }
}

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Python3

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# Python3 program to replace
# every element with the smallest
# of all other array elements
import sys
 
def ReplaceElements(arr, n):
     
    # There should be
    # atleast two elements
    if (n < 2):
        print(" Invalid Input ")
        return
 
    # first stores minimum
    # element of the array
    first = sys.maxsize
 
    # second stores second
    # minimum element of the array
    second = sys.maxsize
 
    # Find the smallest and second
    # smallest elements of the array
    for i in range(n):
 
        # If current element
        # is smaller than first
        # then update both
        # first and second
        if (arr[i] < first):
            second = first
            first = arr[i]
 
        # If arr[i] is in between
        # first and second
        # then update second
        elif (arr[i] < second and
              arr[i] != first):
            second = arr[i]
 
    # Update original array with
    # first and second
    for i in range(n):
        if (arr[i] == first):
            arr[i] = second
        else:
            arr[i] = first
             
    # Print the modified array.
    for i in range(n):
        print(arr[i], end = " ")
 
# Driver code
if __name__ == '__main__':
     
    arr = [ 1, 2, 3, 2 ]
    n = len(arr)
 
    ReplaceElements(arr, n)
 
# This code is contributed by Amit Katiyar

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C#

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// C# program to replace every
// element with the smallest
// of all other array elements
using System;
 
class GFG{
     
static void ReplaceElements(int[] arr, int n)
{
     
    // There should be
    // atleast two elements
    if (n < 2)
    {
        Console.WriteLine(" Invalid Input ");
        return;
    }
 
    // first stores minimum
    // element of the array
    int first = Int32.MaxValue;
 
    // second stores second
    // minimum element of the array
    int second = Int32.MaxValue;
 
    // Find the smallest and second
    // smallest elements of the array
    for(int i = 0; i < n; i++)
    {
         
        // If current element
        // is smaller than first
        // then update both
        // first and second
        if (arr[i] < first)
        {
            second = first;
            first = arr[i];
        }
 
        // If arr[i] is in between
        // first and second
        // then update second
        else if (arr[i] < second &&
                 arr[i] != first)
            second = arr[i];
    }
 
    // Update original array with
    // first and second
    for(int i = 0; i < n; i++)
    {
        arr[i] = (arr[i] == first) ?
                  second : first;
    }
 
    // Print the modified array.
    for(int i = 0; i < n; ++i)
    {
        Console.Write(arr[i] + " ");
    }
}
 
// Driver code
static void Main()
{
    int[] arr = { 1, 2, 3, 2 };
    int n = arr.Length;
 
    ReplaceElements(arr, n);
}
}
 
// This code is contributed by divyeshrabadiya07

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Output: 

2 1 1 1






 

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

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