Insert Element at the Beginning of an Array
Last Updated :
07 Nov, 2024
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Given an array of integers, the task is to insert an element at the beginning of the array.
Examples:
Input: arr[] = [10, 20, 30, 40], ele = 50
Output: [50, 10, 20, 30, 40]Input: arr[] = [], ele = 20
Output: [20]
[Approach 1] Using Built-In Methods
We will use library methods like insert() in C++, Python and C#, add() in Java and unshift() in JavaScript.
// C++ program to insert given element at the beginning
// of an array
#include <iostream>
#include <vector>
using namespace std;
int main() {
vector<int> arr = {10, 20, 30, 40};
int element = 50;
cout << "Array before insertion\n";
for (int i = 0; i < arr.size(); i++)
cout << arr[i] << " ";
// Insert element at the beginning
arr.insert(arr.begin(), element);
cout << "\nArray after insertion\n";
for (int i = 0; i < arr.size(); i++)
cout << arr[i] << " ";
return 0;
}
// Java program to insert a given element at the beginning of an arraY
import java.util.ArrayList;
import java.util.Arrays;
class GfG {
public static void main(String[] args) {
ArrayList<Integer> arr = new
ArrayList<>(Arrays.asList(10, 20, 30, 40));
int element = 50;
System.out.println("Array before insertion");
for (int i = 0; i < arr.size(); i++)
System.out.print(arr.get(i) + " ");
// Insert element at the beginning
arr.add(0, element);
System.out.println("\nArray after insertion");
for (int i = 0; i < arr.size(); i++)
System.out.print(arr.get(i) + " ");
}
}
# Python program to insert a given element at the beginning
# of an array
arr = [10, 20, 30, 40]
element = 50
print("Array before insertion")
for i in range(len(arr)):
print(arr[i], end=" ")
# Insert element at the beginning
arr.insert(0, element)
print("\nArray after insertion")
for i in range(len(arr)):
print(arr[i], end=" ")
// C# program to insert a given element at the beginning
// of an array
using System;
using System.Collections.Generic;
class GfG {
static void Main() {
List<int> arr = new List<int> { 10, 20, 30, 40 };
int element = 50;
Console.WriteLine("Array before insertion");
foreach (int num in arr)
Console.Write(num + " ");
// Insert element at the beginning
arr.Insert(0, element);
Console.WriteLine("\nArray after insertion");
foreach (int num in arr)
Console.Write(num + " ");
}
}
// JavaScript program to insert a given element at the beginning
// of an array
let arr = [10, 20, 30, 40];
let element = 50;
console.log("Array before insertion");
console.log(arr.join(" "));
// Insert element at the beginning
arr.unshift(element);
console.log("Array after insertion");
console.log(arr.join(" "));
Output
Array before insertion 10 20 30 40 Array after insertion 50 10 20 30 40
Time Complexity: O(n), where n is the size of the array.
[Approach 2] Using Custom Method
To insert an element at the beginning of an array, first shift all the elements of the array to the right by 1 index and after shifting insert the new element at 0th position.
// C++ program to insert given element at the beginning
// of an array
#include <iostream>
#include <vector>
using namespace std;
int main() {
vector<int> arr = {10, 20, 30, 40, 0};
int n = 4;
int element = 50;
cout << "Array before insertion\n";
for (int i = 0; i < n; i++)
cout << arr[i] << " ";
// Shift all elements to the right
for(int i = n - 1; i >= 0; i--) {
arr[i + 1] = arr[i];
}
// Insert new element at the beginning
arr[0] = element;
cout << "\nArray after insertion\n";
for (int i = 0; i <= n; i++)
cout << arr[i] << " ";
return 0;
}
// C program to insert given element at the beginning
// of an array
#include <stdio.h>
int main() {
int arr[6] = {10, 20, 30, 40, 0};
int n = 4;
int element = 50;
printf("Array before insertion:\n");
for (int i = 0; i < n; i++) {
printf("%d ", arr[i]);
}
// Shift elements to the right
for (int i = n - 1; i >= 0; i--) {
arr[i + 1] = arr[i];
}
// Insert the new element at the beginning
arr[0] = element;
printf("\nArray after insertion:\n");
for (int i = 0; i <= n; i++) {
printf("%d ", arr[i]);
}
return 0;
}
// Java program to insert given element at the beginning
// of an array
import java.util.Arrays;
class GfG {
public static void main(String[] args) {
int[] arr = {10, 20, 30, 40, 0};
int n = 4;
int element = 50;
System.out.println("Array before insertion");
for (int i = 0; i < n; i++) {
System.out.print(arr[i] + " ");
}
// Shift all elements to the right
for (int i = n - 1; i >= 0; i--) {
arr[i + 1] = arr[i];
}
// Insert new element at the beginning
arr[0] = element;
System.out.println("\nArray after insertion");
for (int i = 0; i <= n; i++) {
System.out.print(arr[i] + " ");
}
}
}
# Python program to insert given element at the beginning
# of an array
arr = [10, 20, 30, 40, 0]
n = 4
element = 50
print("Array before insertion")
for i in range(n):
print(arr[i], end=" ")
# Shift all elements to the right
for i in range(n - 1, -1, -1):
arr[i + 1] = arr[i]
# Insert new element at the beginning
arr[0] = element
print("\nArray after insertion")
for i in range(n + 1):
print(arr[i], end=" ")
// C# program to insert given element at the beginning
// of an array
using System;
class GfG {
static void Main() {
int[] arr = {10, 20, 30, 40, 0};
int n = 4;
int element = 50;
Console.WriteLine("Array before insertion");
for (int i = 0; i < n; i++) {
Console.Write(arr[i] + " ");
}
// Shift all elements to the right
for (int i = n - 1; i >= 0; i--) {
arr[i + 1] = arr[i];
}
// Insert new element at the beginning
arr[0] = element;
Console.WriteLine("\nArray after insertion");
for (int i = 0; i <= n; i++) {
Console.Write(arr[i] + " ");
}
}
}
// JavaScript program to insert given element at the beginning
// of an array
let arr = [10, 20, 30, 40, 0];
let n = 4;
let element = 50;
console.log("Array before insertion");
console.log(arr.slice(0, n).join(" "));
// Shift all elements to the right
for (let i = n - 1; i >= 0; i--) {
arr[i + 1] = arr[i];
}
// Insert new element at the beginning
arr[0] = element;
console.log("Array after insertion");
console.log(arr.join(" "));
Output
Array before insertion 10 20 30 40 Array after insertion 50 10 20 30 40
Time Complexity: O(n), where n is the size of the array.
