Differences between Array and Dictionary Data Structure

Arrays:

• The array is a collection of the same type of elements at contiguous memory locations under the same name. 
• It is easier to access the element in the case of an array. 
• The size is the key issue in the case of an array which must be known in advance so as to store the elements in it. 
• Insertion and deletion operations are costly in the case of an array since the elements are stored at contiguous memory locations. 
• No modification is possible at the runtime after the array is created and memory wastage can also occur if the size of the array is greater than the number of elements stored in the array.

Array representation:

C++

// C++ code for creating an array
#include <iostream>
using namespace std;

// Driver Code
int main()
{

    // Creating an array
    int arr[10]={1,2,3,4,5,6,7,8,9,10};

    // Printing the array
    for (int i = 0; i < 10; i++)
    {
        cout << arr[i] << " ";
    }
    return 0;
}

Java

/*package whatever //do not write package name here */
import java.io.*;

class GFG {
  public static void main (String[] args) {

    // Creating an array
    int arr[] = {1,2,3,4,5,6,7,8,9,10};

    // Printing the array
    for (int i = 0; i < 10; i++){
      System.out.print(arr[i]+" ");
    }
  }
}

// This code is contributed by aadityaburujwale.

Python

# Python code for Creation of Array

# importing "array" for array creation
import array as arr

# creating an array with integer type
a = arr.array('i', [1, 2, 3, 4, 5, 6, 7, 8, 9, 10])

# printing the array
for i in range(0, 10):

    # comma is used to generate spaces
    print(a[i]),

C#

// C# code for creating an array
using System;

// Driver Code
public class GFG {

    static public void Main()
    {

        // Declaring an array
        int[] arr = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

        // Printing the array
        for (int i = 0; i < arr.Length; i++) {
            Console.Write(arr[i] + " ");
        }
    }
}

Javascript

<script>

    // Creating an array
    let arr = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]

    // Printing the array
    for(let i = 0; i < 10; i++){
        document.write(arr[i] + " ");
    }

    // This code is contributed by lokesh

</script>

Output

1 2 3 4 5 6 7 8 9 10 

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

Dictionary:

• A dictionary is a collection of data values. 
• It holds a key: value pair in which we can easily access a value if the key is known. 
• It improves the readability of your code and makes it easier to debug
• It is fast as the access of a value through a key is a constant time operation

Dictionary representation:

C++

// C++ program to demonstrate functionality of unordered_map
#include <iostream>
#include <unordered_map>
using namespace std;

int main()
{
     // Declare a Dictionary
    unordered_map<string, int> my_dict;

    // Adding Elements to the Dictionary
        my_dict["key1"] = 1;
        my_dict["key2"] = 2;
        my_dict["key3"] = 3;

    // Printing the Dictionary
    for (auto key : my_dict)
        cout << "Key: " << key.first << " Value: " << key.second << endl;

}

// This code is contributed by aadityaburujwale.

Java

/*package whatever //do not write package name here */
import java.io.*;
import java.util.*;

class GFG {
    public static void main (String[] args) {

          // Declare a Dictionary
        HashMap<String,Integer> my_dict = new HashMap<>();

         // Adding Elements to the Dictionary
        my_dict.put("key1", 1);
        my_dict.put("key2", 2);
        my_dict.put("key3", 3);

          // Printing the Dictionary
        for(String key:my_dict.keySet()) {
              System.out.println("Key: "+ key +", Value: " + my_dict.get(key));
            }
    }
}

Python

# Declaring and initializing a dictionary
my_dict = {
  "key1": 1,
  "key2": 2,
  "key3": 3
}
# Printing the dictionary

print(my_dict)

C#

using System;
using System.Collections.Generic;
public class GFG {

    static public void Main()
    {
     // Declare a Dictionary
        IDictionary<string, int> my_dict= new Dictionary<string, int>();

     // Adding Elements to the Dictionary
        my_dict.Add("key1", 1);
        my_dict.Add("key2", 2);
        my_dict.Add("key3", 3);

      // Printing the Dictionary
        foreach(var kvp in my_dict) {
          Console.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);
    }
  }
}

Javascript

<script>
// Javascript program to demonstrate functionality of map

// Declare a Dictionary
var my_dict = new Map();

// Adding Elements to the Dictionary
my_dict.set("key1", 1);
my_dict.set("key2", 2);
my_dict.set("key3", 3);

// Printing the Dictionary
console.log(my_dict);

// This  code is contributed by Shubham Singh
</script>

Output

{'key3': 3, 'key2': 2, 'key1': 1}

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

Comparison Between Array and Dictionary:

#	Array	Dictionary
1	Stores just a set of objects	Represents the relationship between pair of objects
2	Lookup time is more in the  case of array O(N)  where N is the size of the array	Lookup time is less compared to an array. Generally, it is O(1)
3	Elements are stored at contiguous memory locations.	Elements may or may not be stored at a contiguous memory location.
4	Items are unordered, changeable, and do allow duplicates	Items are ordered, changeable, and do not allow duplicates
5	Items are not represented as key: value pair	Items are represented as key: value pair
6	The values in the array are of the same data type	The values in dictionary items can be of any data type
7	Values can be accessed randomly without the need for any key	To access a value the key is required