✨ Solve three exercises - Carlos Maldonado

01-basic-cs/index.js

@@ -5,7 +5,17 @@ const assert = require('assert')
 
 const database = require('./database.json')
 
-const total = 0 // TODO
+const total = _.chain(database)
+  .map(userFromDB => userFromDB.hats) // Get only the hats
+  .omitBy(_.isEmpty) // Remove empty array of hats
+  .values() // Get only the array of hats of every user instead of keys
+  .flatten() // Get only one array with all hats
+  .countBy('id') // Count how many of every hat has been purchased
+  .toPairs() // Convert ever object {id: count} to array [id, count]
+  .sortBy(hat => hat[1]) // sort by count (second element of every [id, count] array)
+  .takeRight(3) // Select first three elements
+  .sumBy(hat => hat[1]) // Sum the top three elements
+  .value()
 
 // Throws error on failure
 assert.equal(total, 23, `Invalid result: ${total} != 23`)
@@ -14,6 +24,25 @@ console.log('Success!')
 
 /**
  * Time and space complexity in O() notation is:
- *   - time complexity: TODO
- *   - space complexity: TODO
+ *   - time complexity:
+ * The methods 'map', 'omitBy', 'flatten', 'countBy' and 'toPairs' have a
+ * time complexity of O(n) since the have to access every element of the array
+ * to apply their functions.
+ *
+ * The method 'sortBy' has a time complexity of O(n Log n) since it uses a special
+ * sorting algorithm
+ *
+ * the methods 'takeRight' and 'sumBy' have a time complexity of O(k), where k
+ * is the number of elements to operate.
+ *
+ * In conclusion, the time complexity of this algorithm depends on the length of
+ * the array in the database and the qantity of elements to take into account
+ * in the final sum. In general the time complexity is O(n Log n) due to the method
+ * 'sortBy', wich has the higher time complexity.
+ *
+ *   - space complexity:
+ * In this case, the space complexity is O(n), where n is the number of elements
+ * in the database. This is because every operation in the chain returns a new array,
+ * and, in general (taking worst case scenario), the space required to store these arrays
+ * is proportional to the size of array in the database.
  */

02-nodejs/index.js

@@ -3,10 +3,30 @@
 const express = require('express')
 
 const User = require('./models/User')
+const { Transform } = require('stream')
 
 // Setup Express.js app
 const app = express()
 
-// TODO: everything else
+app.get('/users', (req, res) => {
+  const filename = 'users-db.csv'
+  const users = User.find().batchSize(30).cursor()
+
+  res.setHeader('Content-Disposition', `attachment; filename="${filename}"`)
+  res.setHeader('Content-Type', 'text/csv')
+
+  res.write('id, email, name\n')
+
+  const streamCSV = new Transform({
+    objectMode: true,
+    transform (user, _, done) {
+      const row = `${user.id},${user.email},${user.name}\n`
+      done(null, row)
+    }
+  })
+
+  streamCSV.pipe(res)
+  users.pipe(streamCSV)
+})
 
 app.listen(3000)

03-react/src/App.js

@@ -1,3 +1,4 @@
+import React from 'react'
 import { BrowserRouter, Route, Switch } from 'react-router-dom'
 import Exercise from './components/pages/Exercise'
 

03-react/src/components/pages/Exercise/index.js

@@ -1,45 +1,9 @@
 import './assets/styles.css'
-import { useState } from 'react'
+import { React, useState } from 'react'
+import { movies } from '../../../core/data/movies'
+import { discountRules } from '../../../core/data/discounts'
 
 export default function Exercise01 () {
-  const movies = [
-    {
-      id: 1,
-      name: 'Star Wars',
-      price: 20
-    },
-    {
-      id: 2,
-      name: 'Minions',
-      price: 25
-    },
-    {
-      id: 3,
-      name: 'Fast and Furious',
-      price: 10
-    },
-    {
-      id: 4,
-      name: 'The Lord of the Rings',
-      price: 5
-    }
-  ]
-
-  const discountRules = [
-    {
-      m: [3, 2],
-      discount: 0.25
-    },
-    {
-      m: [2, 4, 1],
-      discount: 0.5
-    },
-    {
-      m: [4, 2],
-      discount: 0.1
-    }
-  ]
-
   const [cart, setCart] = useState([
     {
       id: 1,
@@ -48,27 +12,79 @@ export default function Exercise01 () {
       quantity: 2
     }
   ])
+  const ACTIONS = {
+    INCREMENT: 'INCREMENT',
+    DECREMENT: 'DECREMENT'
+  }
+
+  const getTotal = () => {
+    const moviesInCartIds = cart.map(movie => movie.id)
+    const discountRule = discountRules.find(rule => {
+      return rule.movieIds.length === moviesInCartIds.length && rule.movieIds.every(id => moviesInCartIds.includes(id))
+    })
+
+    const totalWithoutDiscount = cart.reduce((acc, movie) => acc + movie.price * movie.quantity, 0)
+    const total = discountRule ? totalWithoutDiscount * (1 - discountRule.discountPercentage) : totalWithoutDiscount
+
+    return total
+  }
+
+  const getMovieIndexFromCart = (id) => {
+    return cart.findIndex(movieInCart => movieInCart.id === id)
+  }
 
-  const getTotal = () => 0 // TODO: Implement this
+  const addMovieToCart = (movie) => {
+    const cartToSet = [...cart]
+    const existingMovieIndex = getMovieIndexFromCart(movie.id)
+
+    if (existingMovieIndex >= 0) {
+      cartToSet[existingMovieIndex].quantity++
+    } else {
+      cartToSet.push({
+        ...movie,
+        quantity: 1
+      })
+    }
+    setCart(cartToSet)
+  }
+
+  const updateQuantity = (movieId, action) => {
+    const cartToUpdate = [...cart]
+    const movieIndexToUpdate = getMovieIndexFromCart(movieId)
+
+    switch (action) {
+      case ACTIONS.INCREMENT:
+        cartToUpdate[movieIndexToUpdate].quantity++
+        break
+      case ACTIONS.DECREMENT:
+        cartToUpdate[movieIndexToUpdate].quantity > 1
+          ? cartToUpdate[movieIndexToUpdate].quantity--
+          : cartToUpdate.splice(movieIndexToUpdate, 1)
+        break
+      default:
+        break
+    }
+    setCart(cartToUpdate)
+  }
 
   return (
     <section className="exercise01">
       <div className="movies__list">
         <ul>
-          {movies.map(o => (
-            <li className="movies__list-card">
+          {movies.map(movie => (
+            <li className="movies__list-card" key={movie.id}>
               <ul>
                 <li>
-                  ID: {o.id}
+                  ID: {movie.id}
                 </li>
                 <li>
-                  Name: {o.name}
+                  Name: {movie.name}
                 </li>
                 <li>
-                  Price: ${o.price}
+                  Price: ${movie.price}
                 </li>
               </ul>
-              <button onClick={() => console.log('Add to cart', o)}>
+              <button onClick={() => addMovieToCart(movie)}>
                 Add to cart
               </button>
             </li>
@@ -77,27 +93,27 @@ export default function Exercise01 () {
       </div>
       <div className="movies__cart">
         <ul>
-          {cart.map(x => (
-            <li className="movies__cart-card">
+          {cart.map(cartMovie => (
+            <li className="movies__cart-card" key={cartMovie.id}>
               <ul>
                 <li>
-                  ID: {x.id}
+                  ID: {cartMovie.id}
                 </li>
                 <li>
-                  Name: {x.name}
+                  Name: {cartMovie.name}
                 </li>
                 <li>
-                  Price: ${x.price}
+                  Price: ${cartMovie.price}
                 </li>
               </ul>
               <div className="movies__cart-card-quantity">
-                <button onClick={() => console.log('Decrement quantity', x)}>
+                <button onClick={() => updateQuantity(cartMovie.id, ACTIONS.DECREMENT)}>
                   -
                 </button>
                 <span>
-                  {x.quantity}
+                  {cartMovie.quantity}
                 </span>
-                <button onClick={() => console.log('Increment quantity', x)}>
+                <button onClick={() => updateQuantity(cartMovie.id, ACTIONS.INCREMENT)}>
                   +
                 </button>
               </div>

03-react/src/core/data/discounts.js

@@ -0,0 +1,14 @@
+export const discountRules = [
+  {
+    movieIds: [3, 2],
+    discountPercentage: 0.25
+  },
+  {
+    movieIds: [2, 4, 1],
+    discountPercentage: 0.5
+  },
+  {
+    movieIds: [4, 2],
+    discountPercentage: 0.1
+  }
+]

03-react/src/core/data/movies.js

@@ -0,0 +1,22 @@
+export const movies = [
+  {
+    id: 1,
+    name: 'Star Wars',
+    price: 20
+  },
+  {
+    id: 2,
+    name: 'Minions',
+    price: 25
+  },
+  {
+    id: 3,
+    name: 'Fast and Furious',
+    price: 10
+  },
+  {
+    id: 4,
+    name: 'The Lord of the Rings',
+    price: 5
+  }
+]