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joaquinelio merged 28 commits into from
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Arrays #309

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4 changes: 2 additions & 2 deletions 1-js/05-data-types/04-array/1-item-value/solution.md
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The result is `4`:
El resultado es `4`:


```js run
Expand All @@ -13,5 +13,5 @@ alert( fruits.length ); // 4
*/!*
```

That's because arrays are objects. So both `shoppingCart` and `fruits` are the references to the same array.
Esto es porque los arrays son objetos. Entonces ambos, `shoppingCart` y `fruits` son referencias al mismo array.

10 changes: 5 additions & 5 deletions 1-js/05-data-types/04-array/1-item-value/task.md
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Expand Up @@ -2,18 +2,18 @@ importance: 3

---

# Is array copied?
# ¿El array es copiado?

What is this code going to show?
¿Qué va a mostrar este código?

```js
let fruits = ["Apples", "Pear", "Orange"];

// push a new value into the "copy"
// introduce un valor nuevo dentro de una copia
let shoppingCart = fruits;
shoppingCart.push("Banana");

// what's in fruits?
alert( fruits.length ); // ?
// ¿Qué hay en "fruits"?
alert( fruits.length ); // ¿?
```

44 changes: 22 additions & 22 deletions 1-js/05-data-types/04-array/10-maximal-subarray/solution.md
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# Slow solution
# Solución lenta

We can calculate all possible subsums.
Podemos calcular todas las subsumas.

The simplest way is to take every element and calculate sums of all subarrays starting from it.
La forma más simple es tomar cada elemento y calcular las sumas de todos los subarrays que comienzan con él.

For instance, for `[-1, 2, 3, -9, 11]`:
Por ejemplo, para `[-1, 2, 3, -9, 11]`:

```js no-beautify
// Starting from -1:
// Comenzando desde -1:
-1
-1 + 2
-1 + 2 + 3
-1 + 2 + 3 + (-9)
-1 + 2 + 3 + (-9) + 11

// Starting from 2:
// Comenzando desde 2:
2
2 + 3
2 + 3 + (-9)
2 + 3 + (-9) + 11

// Starting from 3:
// Comenzando desde 3:
3
3 + (-9)
3 + (-9) + 11

// Starting from -9
// Comenzando desde -9
-9
-9 + 11

// Starting from 11
// Comenzando desde 11
11
```

The code is actually a nested loop: the external loop over array elements, and the internal counts subsums starting with the current element.
El código es un bucle anidado. El bucle externo itera sobre los elementos del array, y el interno cuenta subsumas comenzando con cada uno de ellos.

```js run
function getMaxSubSum(arr) {
let maxSum = 0; // if we take no elements, zero will be returned
let maxSum = 0; // si no obtenemos elementos, devolverá cero
Comment thread
joaquinelio marked this conversation as resolved.

for (let i = 0; i < arr.length; i++) {
let sumFixedStart = 0;
Expand All @@ -57,25 +57,25 @@ alert( getMaxSubSum([1, 2, 3]) ); // 6
alert( getMaxSubSum([100, -9, 2, -3, 5]) ); // 100
```

The solution has a time complexety of [O(n<sup>2</sup>)](https://en.wikipedia.org/wiki/Big_O_notation). In other words, if we increase the array size 2 times, the algorithm will work 4 times longer.
La solución tiene una complejidad 2 en notación Landau [O(n<sup>2</sup>)](https://es.wikipedia.org/wiki/Notaci%C3%B3n_de_Landau) (coste respecto al tiempo). Es decir, si multiplicamos el tamaño del array por 2, el tiempo del algoritmo se multiplicará por 4.

For big arrays (1000, 10000 or more items) such algorithms can lead to a serious sluggishness.
Para arrays muy grandes (1000, 10000 o más items) tales algoritmos llevarán a una severa lentitud.

# Fast solution
# Solución rápida

Let's walk the array and keep the current partial sum of elements in the variable `s`. If `s` becomes negative at some point, then assign `s=0`. The maximum of all such `s` will be the answer.
Recorramos el array y registremos la suma parcial actual de los elementos en la variable `s`. Si `s` se vuelve cero en algún punto, le asignamos `s=0`. El máximo entre todas las sumas parciales `s` será la respuesta.

If the description is too vague, please see the code, it's short enough:
Si la descripción te resulta demasiado vaga, por favor mira el código. Es bastante corto:

```js run demo
function getMaxSubSum(arr) {
let maxSum = 0;
let partialSum = 0;

for (let item of arr) { // for each item of arr
partialSum += item; // add it to partialSum
maxSum = Math.max(maxSum, partialSum); // remember the maximum
if (partialSum < 0) partialSum = 0; // zero if negative
for (let item of arr) { // por cada item de arr
partialSum += item; // se lo suma a partialSum
maxSum = Math.max(maxSum, partialSum); // registra el máximo
if (partialSum < 0) partialSum = 0; // cero si se vuelve negativo
}

return maxSum;
Expand All @@ -89,6 +89,6 @@ alert( getMaxSubSum([1, 2, 3]) ); // 6
alert( getMaxSubSum([-1, -2, -3]) ); // 0
```

The algorithm requires exactly 1 array pass, so the time complexity is O(n).
El algoritmo requiere exactamente una pasada, entonces la complejidad es O(n).

You can find more detail information about the algorithm here: [Maximum subarray problem](http://en.wikipedia.org/wiki/Maximum_subarray_problem). If it's still not obvious why that works, then please trace the algorithm on the examples above, see how it works, that's better than any words.
Puedes encontrar información detallada acerca del algoritmo: [Subvector de suma máxima](https://es.wikibooks.org/wiki/Algoritmia/Divide_y_vencer%C3%A1s#Subvector_de_suma_m%C3%A1xima). Si aún no es obvio cómo funciona, traza el algoritmo en los ejemplos de arriba y observa cómo trabaja, es mejor que cualquier explicación.
18 changes: 9 additions & 9 deletions 1-js/05-data-types/04-array/10-maximal-subarray/task.md
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---

# A maximal subarray
# Subarray máximo

The input is an array of numbers, e.g. `arr = [1, -2, 3, 4, -9, 6]`.
La entrada es un array de números, por ejemplo `arr = [1, -2, 3, 4, -9, 6]`.

The task is: find the contiguous subarray of `arr` with the maximal sum of items.
La tarea es: encuentra el subarray contiguo de items de `arr` con la suma máxima.

Write the function `getMaxSubSum(arr)` that will return that sum.
Escribe la función `getMaxSubSum(arr)` que devuelva tal sumo.

For instance:
Por ejemplo:

```js
getMaxSubSum([-1, *!*2, 3*/!*, -9]) == 5 (the sum of highlighted items)
getMaxSubSum([-1, *!*2, 3*/!*, -9]) == 5 (la suma de items resaltados)
getMaxSubSum([*!*2, -1, 2, 3*/!*, -9]) == 6
getMaxSubSum([-1, 2, 3, -9, *!*11*/!*]) == 11
getMaxSubSum([-2, -1, *!*1, 2*/!*]) == 3
getMaxSubSum([*!*100*/!*, -9, 2, -3, 5]) == 100
getMaxSubSum([*!*1, 2, 3*/!*]) == 6 (take all)
getMaxSubSum([*!*1, 2, 3*/!*]) == 6 (toma todo)
```

If all items are negative, it means that we take none (the subarray is empty), so the sum is zero:
Si todos los elementos son negativos, significa que que no tomamos ninguno (el subarray está vacío), entonces la suma es cero:

```js
getMaxSubSum([-1, -2, -3]) = 0
```

Please try to think of a fast solution: [O(n<sup>2</sup>)](https://en.wikipedia.org/wiki/Big_O_notation) or even O(n) if you can.
Trata de pensar un solución rápida: [O(n<sup>2</sup>)](https://es.wikipedia.org/wiki/Notaci%C3%B3n_de_Landau) o incluso O(n) si puedes.
17 changes: 8 additions & 9 deletions 1-js/05-data-types/04-array/2-create-array/task.md
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Expand Up @@ -2,17 +2,17 @@ importance: 5

---

# Array operations.
# Operaciones en arrays.

Let's try 5 array operations.
Tratemos 5 operaciones de array.

1. Create an array `styles` with items "Jazz" and "Blues".
2. Append "Rock-n-Roll" to the end.
3. Replace the value in the middle by "Classics". Your code for finding the middle value should work for any arrays with odd length.
4. Strip off the first value of the array and show it.
5. Prepend `Rap` and `Reggae` to the array.
1. Crear un array `styles` con los items "Jazz" y "Blues".
2. Agregar "Rock-n-Roll" al final.
3. Reemplazar el valor en el medio por "Classics". Tu código para encontrar el valor medio debe funcionar con cualquier array de longitud impar.
4. Quitar el primer valor del array y mostrarlo.
5. Anteponer `Rap` y `Reggae` al array.

The array in the process:
El array durante el proceso:

```js no-beautify
Jazz, Blues
Expand All @@ -21,4 +21,3 @@ Jazz, Classics, Rock-n-Roll
Classics, Rock-n-Roll
Rap, Reggae, Classics, Rock-n-Roll
```

6 changes: 3 additions & 3 deletions 1-js/05-data-types/04-array/3-call-array-this/solution.md
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The call `arr[2]()` is syntactically the good old `obj[method]()`, in the role of `obj` we have `arr`, and in the role of `method` we have `2`.
El llamado a `arr[2]()` es sintácticamente el buen y viejo `obj[method]()`, en el rol de `obj` tenemos `arr`, y en el rol de `method` tenemos `2`.

So we have a call of the function `arr[2]` as an object method. Naturally, it receives `this` referencing the object `arr` and outputs the array:
Entonces tenemos una llamada a función `arr[2]` como un método de objeto. Naturalmente, recibe `this` referenciando el objeto `arr` y su salida es el array:

```js run
let arr = ["a", "b"];
Expand All @@ -12,4 +12,4 @@ arr.push(function() {
arr[2](); // a,b,function(){...}
```

The array has 3 values: initially it had two, plus the function.
El array tiene 3 valores: Iniciamente tenía 2 y se agregó la función.
5 changes: 2 additions & 3 deletions 1-js/05-data-types/04-array/3-call-array-this/task.md
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---

# Calling in an array context
# LLamados en un contexto de array

What is the result? Why?
¿Cuál es el resultado y por qué?

```js
let arr = ["a", "b"];
Expand All @@ -15,4 +15,3 @@ arr.push(function() {

arr[2](); // ?
```

7 changes: 3 additions & 4 deletions 1-js/05-data-types/04-array/5-array-input-sum/solution.md
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Please note the subtle, but important detail of the solution. We don't convert `value` to number instantly after `prompt`, because after `value = +value` we would not be able to tell an empty string (stop sign) from the zero (valid number). We do it later instead.
Toma nota del sutil pero importante detalle de la solución. No convertimos `value` a número instantáneamente después de `prompt`, porque después de `value = +value` no seríamos capaces de diferenciar una cadena vacía (señal de detención) de un cero (un número válido). Lo hacemos más adelante.


```js run demo
Expand All @@ -8,9 +8,9 @@ function sumInput() {

while (true) {

let value = prompt("A number please?", 0);
let value = prompt("Un número, por favor...", 0);

// should we cancel?
// ¿Debemos cancelar?
if (value === "" || value === null || !isFinite(value)) break;

numbers.push(+value);
Expand All @@ -25,4 +25,3 @@ function sumInput() {

alert( sumInput() );
```

12 changes: 6 additions & 6 deletions 1-js/05-data-types/04-array/5-array-input-sum/task.md
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Expand Up @@ -2,14 +2,14 @@ importance: 4

---

# Sum input numbers
# Suma de números ingresados

Write the function `sumInput()` that:
Escribe una función `sumInput()` que:

- Asks the user for values using `prompt` and stores the values in the array.
- Finishes asking when the user enters a non-numeric value, an empty string, or presses "Cancel".
- Calculates and returns the sum of array items.
- Pida al usuario valores usando `prompt` y los almacene en el array.
- Termine de pedirlos cuando el usuario ingrese un valor no numérico, una cadena vacía, o presione "Escape".
- Calcule y devuelva la suma de los items del array.

P.S. A zero `0` is a valid number, please don't stop the input on zero.
P.D. Un cero `0` es un número válido, por favor no detengas los ingresos con el cero.

[demo]
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