Replace every element with the smallest element on its left side

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

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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 
?> 

Output:

-1 4 4 2 1 1

Time Complexity: O(N)

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My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

PHP

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