How to increment array index in javascript

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Given an array arr[], the task is increment all the odd positioned elements by 1 and decrement all the even positioned elements by 1.

Examples: 

Input: arr[] = {3, 6, 8} 
Output: 4 5 9

Input: arr[] = {9, 7, 3} 
Output: 10 6 4

Approach: Traverse the array element by element and if the current element’s position is odd then increment it by 1 else decrement it by 1. Print the contents of the updated array in the end.

Below is the implementation of the above approach:  

C++

#include <bits/stdc++.h>

using namespace std;

void printArr(int arr[], int n)

{

    for (int i = 0; i < n; i++)

        cout << arr[i] << " ";

}

void updateArr(int arr[], int n)

{

    for (int i = 0; i < n; i++)

        if ((i + 1) % 2 == 1)

            arr[i]++;

        else

            arr[i]--;

    printArr(arr, n);

}

int main()

{

    int arr[] = { 3, 6, 8 };

    int n = sizeof(arr) / sizeof(arr[0]);

    updateArr(arr, n);

    return 0;

}

Java

class GfG

{

static void printArr(int arr[], int n)

{

    for (int i = 0; i < n; i++)

        System.out.print(arr[i] + " ");

}

static void updateArr(int arr[], int n)

{

    for (int i = 0; i < n; i++)

        if ((i + 1) % 2 == 1)

            arr[i]++;

        else

            arr[i]--;

    printArr(arr, n);

}

public static void main(String[] args)

{

    int arr[] = { 3, 6, 8 };

    int n = arr.length;

    updateArr(arr, n);

}

}

Python3

def printArr(arr, n):

    for i in range(0, n):

        print(arr[i], end = " ");

def updateArr(arr, n):

    for i in range(0, n):

        if ((i + 1) % 2 == 1):

            arr[i] += 1;

        else:

            arr[i] -= 1;

    printArr(arr, n);

if __name__ == '__main__':

    arr = [3, 6, 8];

    n = len(arr);

    updateArr(arr, n);

C#

class GfG

{

static void printArr(int []arr, int n)

{

    for (int i = 0; i < n; i++)

        System.Console.Write(arr[i] + " ");

}

static void updateArr(int []arr, int n)

{

    for (int i = 0; i < n; i++)

        if ((i + 1) % 2 == 1)

            arr[i]++;

        else

            arr[i]--;

    printArr(arr, n);

}

static void Main()

{

    int []arr = { 3, 6, 8 };

    int n = arr.Length;

    updateArr(arr, n);

}

}

PHP

<?php

function printArr($arr, $n)

{

    for ($i = 0; $i < $n; $i++)

        echo $arr[$i] . " ";

}

function updateArr($arr, $n)

{

    for ($i = 0; $i < $n; $i++)

        if (($i + 1) % 2 == 1)

            $arr[$i]++;

        else

            $arr[$i]--;

    printArr($arr, $n);

}

$arr = array( 3, 6, 8 );

$n = count($arr);

updateArr($arr, $n);

?>

Javascript

<script>

function printArr(arr, n)

{

     var i;

    for (i = 0; i < n; i++)

      document.write(arr[i] + " ");

}

function updateArr(arr, n)

{

    var i;

    for (i = 0; i < n; i++)

        if ((i + 1) % 2 == 1)

            arr[i]++;

        else

            arr[i]--;

    printArr(arr, n);

}

    var arr = [3, 6, 8];

    var n = arr.length;

    updateArr(arr, n);

</script>

Time Complexity: O(n)

Auxiliary Space: O(1)