HashTables.js

//implement associated arrays and mapping of key, value pair
//common way to implement map data structure and objects
//Time complexity : average is O(1) / worst case is O(n)
//has problem of collision = to solve it, just store both key and value there

let hash = (string, max) => {
  let hash = 0;
  for (let i = 0; i < string.length; i++) {
    hash += string.charCodeAt(i);
  }
  return hash % max;
};

let HashTable = function () {
  let storage = [];
  const storageLimit = 4;
  this.print = function () {
    console.log(storage);
  };
  this.add = function (key, value) {
    let index = hash(key, storageLimit);
    if (storage[index] === undefined) {
      storage[index] = [[key, value]];
    } else {
      let inserted = false;
      for (let i = 0; i < storage[index].length; i++) {
        if (storage[index][i][0] === key) {
          storage[index][i][1] = value;
          inserted = true;
        }
      }
      if (inserted === false) {
        storage[index].push([key, value]);
      }
    }
  };
  this.remove = function (key) {
    let index = hash(key, storageLimit);
    if (storage[index].length === 1 && storage[index][0][0] === key) {
      delete storage[index];
    } else {
      for (let i = 0; i < storage[index].length; i++) {
        if (storage[index][i][0] === key) {
          delete storage[index][i];
        }
      }
    }
  };
  this.lookup = function (key) {
    let index = hash(key, storageLimit);
    if (storage[index] === undefined) {
      return undefined;
    } else {
      for (let i = 0; i < storage[index].length; i++) {
        if (storage[index][i][0] === key) {
          return storage[index][i][1];
        }
      }
    }
  };
};