Hash.js

/*

A JavaScript program for creating a well known data structure "Hash Table". A hash table (often called a hash map) is a data structure 
that maps keys to values. Hash tables combine lookup, insert, and delete operations in an efficient way. Hash tables can perform in constant time.
In the worst-case scenario, the performance of hash tables can be as low as O(n).

In this program, user can provide a choice to perform operations on a Hash Table. It is created using a ES6 class syntax. 
prompt & colors are node packages for taking user input and displaying text in different colors respectively. 

*/

const prompt = require("prompt-sync")({ sigint: true });
const colors = require("colors");

// Setting the Color schema
colors.setTheme({
  display: "green",
  insert: "white",
  delete: "red",
  leave: "yellow",
  end: "rainbow",
  wrong: "america",
});

class HashTable {
  constructor(size) {
    // Set Hash Table size
    this.data = new Array(size);
  }

  // Generate a location using simple hash logic
  _hash(key) {
    let hash = 0;
    for (let i = 0; i < key.length; i++) {
      // Location mapping
      hash = (hash + key.charCodeAt(i) + i) % this.data.length;
    }

    return hash;
  }

  // Set the location of item in hash
  set(key, value) {
    let address = this._hash(key);
    if (!this.data[address]) {
      this.data[address] = [];
    }

    // Insert item at the desired location with [key, value] pair
    this.data[address].push([key, value]);
    return this.data;
  }

  // Get the location of item in hash table
  get(key) {
    let address = this._hash(key);
    const currentBucket = this.data[address];
    // Item at the location is not found , return undefined
    if (!currentBucket) return undefined;

    if (currentBucket.length) {
      for (let i = 0; i < currentBucket.length; i++) {
        if (currentBucket[i][0] === key) {
          return {
            data: [currentBucket[i][0], currentBucket[i][1]],
            location: address,
          };
        }
      }
    }
    return undefined;
  }

  // Delete item
  deleteItem(value) {
    let item = this.get(value);

    // Item is not present in hash table
    if (item === undefined)
      return console.log("Can't delete, no such item found");

    // Delete item present at that location from hash table
    delete this.data[item.location];
    return console.log("Deleted", item.data[0]);
  }

  // Display all items
  keys() {
    const keysArray = [];
    for (let i = 0; i < this.data.length; i++) {
      if (this.data[i]) keysArray.push(this.data[i][0][0]);
    }

    return keysArray;
  }
}

// Instantiating the HashTable
const myHashTable = new HashTable(100);

// Insert item in Hash Table
myHashTable.set("grapes", 1000); // Output - [['grapes', 1000]]
myHashTable.set("apple", 100); // Output - [['apple', 100], ['grapes', 1000]]
myHashTable.set("oranges", 50); // Output - [['apple', 100], ['grapes', 1000], ['oranges', 50]]

myHashTable.deleteItem("apple"); // Output - [['grapes', 1000], ['oranges', 50]]
myHashTable.deleteItem("fruits"); // Output - Can't delete, no such item found

let choice = 0;
let value, index;

// Asking user input for performing operations on Hash Table
do {
  console.log("\nWelcome to the Hash Table");
  console.log("Follow the instructions to get in the show");
  console.log("0. To exit without doing anything".yellow);
  console.log("1. Display all elements of the Hash Table".display);
  console.log("2. Insert element in the Hash Table".insert);
  console.log("3. Find element in Hash Table".display);
  console.log("4. Delete element from Hash Table".delete);

  choice = +prompt("Enter your choice - ");

  switch (choice) {
    case 0:
      console.log("Hmm, matter of choice!\n".rainbow);
      return;

    case 1:
      console.log("Hash Table - ", myHashTable.keys());
      break;

    case 2:
      value = prompt("Enter Value ( first value )  to Insert element - ");
      index = +prompt("Enter amount ( second value) to Insert element - ");

      if (index <= 0)
        return console.log("You know this is wrong, Bbye!\n".wrong);

      myHashTable.set(value, index);
      console.log("After Insertion Hash Table - ", myHashTable.keys());
      break;

    case 3:
      if (myHashTable.data.length === 0) {
        return console.log("Hash Table in empty".wrong);
      }

      value = prompt("Enter Value to find the element - ");
      let result = myHashTable.get(value);

      if (!result) console.log("Element not found");
      else console.log("Element ", result);
      break;

    case 4:
      if (myHashTable.data.length === 0) {
        return console.log(
          "404, you can't remove anything from empty hash table".wrong
        );
      }

      value = prompt("Enter Value to delete - ");
      myHashTable.deleteItem(value);
      console.log("After Deletion Hash Table - ", myHashTable.keys());
      break;

    default:
      console.log("You know this is wrong, Bbye!\n".wrong);
      return;
  }
} while (choice !== 0);


// Sample I/O of the above program -

/*

> node Hash

Welcome to the Hash Table
Follow the instructions to get in the show
0. To exit without doing anything
1. Display all elements of the Hash Table
2. Insert element in the Hash Table
3. Find element in Hash Table
4. Delete element from Hash Table
Enter your choice - 1
Hash Table -  [ 'grapes', 'oranges' ]

Welcome to the Hash Table
Follow the instructions to get in the show
0. To exit without doing anything
1. Display all elements of the Hash Table
2. Insert element in the Hash Table
3. Find element in Hash Table
4. Delete element from Hash Table
Enter your choice - 2
Enter Value ( first value )  to Insert element - Icecream
Enter amount ( second value) to Insert element - 250
After Insertion Hash Table -  [ 'Icecream', 'grapes', 'oranges' ]

Welcome to the Hash Table
Follow the instructions to get in the show
0. To exit without doing anything
1. Display all elements of the Hash Table
2. Insert element in the Hash Table
3. Find element in Hash Table
4. Delete element from Hash Table
Enter your choice - 3
Enter Value to find the element - grapes
Element  { data: [ 'grapes', 1000 ], location: 57 }

Welcome to the Hash Table
Follow the instructions to get in the show
0. To exit without doing anything
1. Display all elements of the Hash Table
2. Insert element in the Hash Table
3. Find element in Hash Table
4. Delete element from Hash Table
Enter your choice - 4
Enter Value to delete - grapes
Deleted grapes
After Deletion Hash Table -  [ 'Icecream', 'oranges' ]

Welcome to the Hash Table
Follow the instructions to get in the show
0. To exit without doing anything
1. Display all elements of the Hash Table
2. Insert element in the Hash Table
3. Find element in Hash Table
4. Delete element from Hash Table
Enter your choice - 0
Hmm, matter of choice!

*/