Replace every element with the smallest element on its left side

Difficulty Level : Basic
Last Updated : 12 Apr, 2021

Given an array of integers, the task is to replace every element with the smallest element on its left side.
Note: Replace the first element with -1 as it has no element in its left.
Examples:

Input: arr[] = {4, 5, 2, 1, 7, 6}
Output: -1 4 4 2 1 1
Since, 4 has no element in its left, so replace it by -1.
For 5, 4 is the smallest element in its left.
For 2, 4 is the smallest element in its left.
For 1, 2 is the smallest element in its left.
For 7, 1 is the smallest element in its left.
For 6, 1 is the smallest element in its left.

Input: arr[] = {3, 2, 5, 7, 1}
Output: -1 3 2 2 2

Approach:

Maintain a variable min_ele which will store the smallest element.
Initially, min_ele will be equal to the element at the 0th index.
First replace arr[0] with -1 then traverse the array
And then replace the element with the min_ele value and update the min_ele if the element is smaller than min_ele.
Print the modified array.

Below is the implementation of the above approach:

C++

// C++ program to Replace every
// element with the smaller element
// on its left side
#include <bits/stdc++.h>
using namespace std;
 
// Function to replace the elements
void ReplaceElements(int arr[], int n)
{
    // MIN value initialised
    // to element at 0th index
    int min_ele = arr[0];
    arr[0] = -1;
 
    for (int i = 1; i < n; ++i) {
 
        // If min_ele is smaller than arr[i]
        // then just replace arr[i] with min_ele
        if (min_ele < arr[i])
            arr[i] = min_ele;
 
 
        // Else if update the min_ele also
        else if (min_ele >= arr[i]) {
            int temp = arr[i];
            arr[i] = min_ele;
            min_ele = temp;
        }
    }
}
 
// Driver code
int main()
{
    int arr[] = { 4, 5, 2, 1, 7, 6 };
    int n = sizeof(arr) / sizeof(arr[0]);
 
    // Replace the elements
    // with the smaller element
    // on its left side
    ReplaceElements(arr, n);
 
    // Print the modified array
    for (int i = 0; i < n; ++i)
        cout << arr[i] << " ";
 
    return 0;
}

Java

// Java program to Replace every
// element with the smaller element
// on its left side
 
class GFG {
 
// Function to replace the elements
    static void ReplaceElements(int arr[], int n) {
        // MIN value initialised
        // to element at 0th index
        int min_ele = arr[0];
        arr[0] = -1;
 
        for (int i = 1; i < n; ++i) {
 
            // If min_ele is smaller than arr[i]
            // then just replace arr[i] with min_ele
            if (min_ele < arr[i]) {
                arr[i] = min_ele;
            } // Else if update the min_ele also
            else if (min_ele >= arr[i]) {
                int temp = arr[i];
                arr[i] = min_ele;
                min_ele = temp;
            }
        }
    }
 
// Driver code
    public static void main(String[] args) {
        int arr[] = {4, 5, 2, 1, 7, 6};
        int n = arr.length;
 
        // Replace the elements
        // with the smaller element
        // on its left side
        ReplaceElements(arr, n);
 
        // Print the modified array
        for (int i = 0; i < n; ++i) {
            System.out.print(arr[i] + " ");
        }
    }
}
 
// This code is contributed by Rajput-JI

Python3

# Python3 program to Replace every
# element with the smaller element
# on its left side
 
# Function to replace the elements
def ReplaceElements(arr, n):
 
    # MIN value initialised
    # to element at 0th index
    min_ele = arr[0]
    arr[0] = -1
 
    for i in range(1, n):
 
        # If min_ele is smaller than arr[i]
        # then just replace arr[i] with min_ele
        if (min_ele < arr[i]):
            arr[i] = min_ele
 
        # Else if update the min_ele also
        elif (min_ele >= arr[i]) :
            temp = arr[i]
            arr[i] = min_ele
            min_ele = temp
 
# Driver code
if __name__ == "__main__":
 
    arr = [ 4, 5, 2, 1, 7, 6 ]
    n = len (arr)
 
    # Replace the elements
    # with the smaller element
    # on its left side
    ReplaceElements(arr, n)
 
    # Print the modified array
    for i in range( n):
        print (arr[i], end = " ")
 
# This code is contributed
# by ChitraNayal

C#

// C# program to Replace every
// element with the smaller element
// on its left side
using System;
public class GFG {
 
// Function to replace the elements
    static void ReplaceElements(int []arr, int n) {
        // MIN value initialised
        // to element at 0th index
        int min_ele = arr[0];
        arr[0] = -1;
 
        for (int i = 1; i < n; ++i) {
 
            // If min_ele is smaller than arr[i]
            // then just replace arr[i] with min_ele
            if (min_ele < arr[i]) {
                arr[i] = min_ele;
            } // Else if update the min_ele also
            else if (min_ele >= arr[i]) {
                int temp = arr[i];
                arr[i] = min_ele;
                min_ele = temp;
            }
        }
    }
 
// Driver code
    public static void Main() {
        int []arr = {4, 5, 2, 1, 7, 6};
        int n = arr.Length;
 
        // Replace the elements
        // with the smaller element
        // on its left side
        ReplaceElements(arr, n);
 
        // Print the modified array
        for (int i = 0; i < n; ++i) {
            Console.Write(arr[i] + " ");
        }
    }
}
 
// This code is contributed by Rajput-JI

PHP

<?php
// PHP program to Replace every
// element with the smaller element
// on its left side
 
// Function to replace the elements
function ReplaceElements($arr, $n)
{
    // MIN value initialised
    // to element at 0th index
    $min_ele = $arr[0];
    $arr[0] = -1;
 
    for ($i = 1; $i < $n; ++$i)
    {
 
        // If min_ele is smaller than arr[i]
        // then just replace arr[i] with min_ele
        if ($min_ele < $arr[$i])
            $arr[$i] = $min_ele;
 
        // Else if update the min_ele also
        else if ($min_ele >= $arr[$i])
        {
            $temp = $arr[$i];
            $arr[$i] = $min_ele;
            $min_ele = $temp;
        }
    }
    return $arr;
}
 
// Driver code
$arr = array(4, 5, 2, 1, 7, 6);
$n = sizeof($arr);
 
// Replace the elements
// with the smaller element
// on its left side
$arr1 = ReplaceElements($arr, $n);
 
// Print the modified array
for ($i = 0; $i < $n; ++$i)
    echo $arr1[$i] . " ";
 
// This code is contributed
// by Akanksha Rai
?>

Javascript

<script>
      // JavaScript program to Replace every
      // element with the smaller element
      // on its left side
 
      // Function to replace the elements
      function ReplaceElements(arr, n)
      {
       
        // MIN value initialised
        // to element at 0th index
        var min_ele = arr[0];
        arr[0] = -1;
 
        for (var i = 1; i < n; ++i)
        {
         
          // If min_ele is smaller than arr[i]
          // then just replace arr[i] with min_ele
          if (min_ele < arr[i]) arr[i] = min_ele;
          // Else if update the min_ele also
          else if (min_ele >= arr[i])
          {
            var temp = arr[i];
            arr[i] = min_ele;
            min_ele = temp;
          }
        }
      }
 
      // Driver code
      var arr = [4, 5, 2, 1, 7, 6];
      var n = arr.length;
 
      // Replace the elements
      // with the smaller element
      // on its left side
      ReplaceElements(arr, n);
 
      // Print the modified array
      for (var i = 0; i < n; ++i) document.write(arr[i] + " ");
       
      // This code is contributed by rdtank.
    </script>

Output:

-1 4 4 2 1 1

Time Complexity: O(N)

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