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‎README.md‎

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## License
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This repository is intended for personal use and the content within is not subject to a formal license. However, please be respectful of any code or ideas that may be derived from other sources.
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This repository is intended for personal use and the content within is not subject to a formal license. However, please be respectful of any code or ideas that may be derived from other sources.
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# JavaScript Array Notes
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## Fundamentals
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* **Definition:** Arrays are ordered collections of values. They can hold values of any data type (including other arrays).
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* **Creation:**
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* `let myArray = [];` (Empty array)
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* `let myArray = [1, 2, "three", { key: "value" }];` (Array with mixed data types)
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* `let myArray = new Array(1, 2, 3);` (Using the `Array` constructor)
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* **Indexing:** Elements are accessed using zero-based indexing (e.g., `myArray[0]` for the first element).
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* **Length:** The `length` property returns the number of elements in the array.
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## Common Array Methods
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### Modification
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* **`push(element)`:** Adds an element to the end of the array. Returns the new length.
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* **`pop()`:** Removes the last element from the array. Returns the removed element.
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* **`unshift(element)`:** Adds an element to the beginning of the array. Returns the new length.
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* **`shift()`:** Removes the first element from the array. Returns the removed element.
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* **`splice(startIndex, deleteCount, ...items)`:**
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* Removes elements from `startIndex` with `deleteCount`.
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* Inserts `items` at `startIndex`.
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* Returns an array of the removed elements.
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* **`fill(value, startIndex, endIndex)`:** Fills a portion of the array with a static value.
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* **`reverse()`:** Reverses the order of the elements in the array. Modifies the original array.
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* **`sort(compareFunction)`:** Sorts the elements of the array. Modifies the original array.
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* If `compareFunction` is omitted, elements are sorted lexicographically (string comparison).
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* For numeric sorting: `array.sort((a, b) => a - b);` (ascending), `array.sort((a,b) => b-a);` (descending)
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### Access and Transformation
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* **`slice(startIndex, endIndex)`:** Returns a shallow copy of a portion of the array. Does not modify the original array.
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* **`concat(...arrays)`:** Returns a new array that is the concatenation of the original array and the given arrays. Does not modify the original arrays.
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* **`join(separator)`:** Returns a string by concatenating all of the elements in an array, separated by the specified separator.
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* **`indexOf(element, startIndex)`:** Returns the first index at which a given element can be found in the array, or -1 if it is not present.
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* **`lastIndexOf(element, startIndex)`:** Returns the last index at which a given element can be found in the array, or -1 if it is not present.
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* **`includes(element, startIndex)`:** Determines whether an array includes a certain element, returning `true` or `false`.
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* **`toString()`:** Returns a string representing the array and its elements.
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### Iteration
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* **`forEach(callback)`:** Executes a provided function once for each array element.
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* **`map(callback)`:** Creates a new array with the results of calling a provided function on every element in the calling array.
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* **`filter(callback)`:** Creates a new array with all elements that pass the test implemented by the provided function.
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* **`reduce(callback, initialValue)`:** Executes a reducer function (provided by you) on each element of the array, resulting in a single output value.
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* **`reduceRight(callback, initialValue)`:** Applies a function against an accumulator and each value of the array (from right-to-left) to reduce it to a single value.
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* **`some(callback)`:** Tests whether at least one element in the array passes the test implemented by the provided function. Returns a Boolean value.
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* **`every(callback)`:** Tests whether all elements in the array pass the test implemented by the provided function. Returns a Boolean value.
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* **`find(callback)`:** Returns the value of the first element in the provided array that satisfies the provided testing function.
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* **`findIndex(callback)`:** Returns the index of the first element in the array that satisfies the provided testing function. Otherwise, it returns -1.
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* **`entries()`:** Returns a new Array Iterator object that contains the key/value pairs for each index in the array.
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## Destructuring Arrays
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* `let [first, second, ...rest] = myArray;` (Extracts elements into variables)
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## Spread Operator
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* `let newArray = [...myArray, 4, 5];` (Creates a new array with elements from `myArray` and additional elements)
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## Array-like Objects
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* `arguments` object in functions.
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* DOM NodeLists.
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* Can be converted to arrays using `Array.from()` or the spread operator.
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## Multidimensional Arrays
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* Arrays containing other arrays.
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* Access elements using multiple indices (e.g., `my2DArray[row][column]`).
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## Things to remember for Interviews
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* Array methods are crucial. Practice using `map`, `filter`, `reduce`, `forEach`, and `sort`.
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* Understand the difference between methods that modify the original array and those that return a new array.
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* Be comfortable with array destructuring and the spread operator.
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* Know how to handle array-like objects.
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* Understand the time complexity of common array operations.

‎array/array_notes.js‎

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/*
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Arrays are ordered collections of values. They can hold values of any data type (including other arrays).
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*/
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let arr = []; // empty array
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arr = [1, 2, "three", { key: "value" }];
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console.log("myArray:", arr);
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console.log("myArray[0]:", arr[0]);
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console.log("myArray.length:", arr.length);
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// Modification
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console.log("\n--- Modification ---");
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arr.push(4);
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console.log("push(4):", arr);
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arr.pop();
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console.log("pop():", arr);
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arr.unshift(0);
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console.log("unshift(0):", arr);
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arr.shift();
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console.log("shift():", arr);
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arr.splice(1, 1, "two-changed");
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console.log("splice(1, 1, 'two-changed'):", arr);
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arr.reverse();
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console.log("reverse():", arr);
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arr.sort();
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console.log("sort():", arr); // sorts alphabetically, so the object will be at the start
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let numberArray = [5, 2, 9, 1, 5, 6];
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numberArray.sort((a, b) => a - b);
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console.log("numberArray.sort((a, b) => a - b):", numberArray);
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numberArray.sort((a, b) => b - a);
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console.log("numberArray.sort((a,b) => b-a):", numberArray);
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// Access and Transformation
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console.log("\n--- Access and Transformation ---");
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let slicedArray = arr.slice(1, 3);
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console.log("slice(1, 3):", slicedArray);
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console.log("original myArray:", arr); // slice doesn't modify original
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let concatenatedArray = arr.concat([5, 6]);
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console.log("concat([5, 6]):", concatenatedArray);
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console.log("original myArray:", arr); // concat doesn't modify original
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console.log("join(', '):", arr.join(", "));
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console.log("indexOf('two-changed'):", arr.indexOf("two-changed"));
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console.log("includes('two-changed'):", arr.includes("two-changed"));
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// Iteration
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console.log("\n--- Iteration ---");
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arr.forEach((element, index) => {
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console.log("forEach:", index, element);
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});
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let mappedArray = arr.map((element) => {
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if (typeof element === 'string') {
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return element.toUpperCase();
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}
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return element;
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});
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console.log("map():", mappedArray);
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let filteredArray = numberArray.filter((element) => element > 3);
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console.log("filter():", filteredArray);
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let reducedValue = numberArray.reduce((accumulator, currentValue) => accumulator + currentValue, 0);
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console.log("reduce():", reducedValue);
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let someResult = numberArray.some((element) => element > 8);
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console.log("some():", someResult);
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let everyResult = numberArray.every((element) => element > 0);
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console.log("every():", everyResult);
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let foundElement = numberArray.find((element) => element === 5);
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console.log("find():", foundElement);
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let foundIndex = numberArray.findIndex((element) => element === 9);
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console.log("findIndex():", foundIndex);
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// Destructuring Arrays
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console.log("\n--- Destructuring Arrays ---");
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let [first, second, ...rest] = arr;
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console.log("destructuring:", first, second, rest);
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// Spread Operator
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console.log("\n--- Spread Operator ---");
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let newArray = [...arr, 4, 5];
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console.log("spread:", newArray);
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// Multidimensional Arrays
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console.log("\n--- Multidimensional Arrays ---");
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let multiArray = [[1, 2], [3, 4], [5, 6]];
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console.log("multiArray:", multiArray);
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console.log("multiArray[1][0]:", multiArray[1][0]);
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// Array.from
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console.log("\n--- Array.from ---");
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function arrayFromExample() {
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const args = Array.from(arguments);
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console.log(args)
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}
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arrayFromExample(1, 2, 3, 4);

‎old/BEDataTest/1.2.js‎

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remove("Hi!") === "Hi"
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remove("Hi!!!") === "Hi!!"
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remove("!Hi") === "!Hi"
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remove("!Hi!") === "!Hi"
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remove("Hi! Hi!") === "Hi! Hi"
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remove("Hi") === "Hi"
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function remove(string) {
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return string.endsWith('!') ? string.substr(0, string.length - 1) : string;
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}

‎old/BEDataTest/1.js‎

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remove("Hi!") === "Hi"
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remove("Hi!!!") === "Hi!!"
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remove("!Hi") === "!Hi"
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remove("!Hi!") === "!Hi"
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remove("Hi! Hi!") === "Hi! Hi"
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remove("Hi") === "Hi"
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function remove(str) {
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// Assumed that str would be string anyway
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last_ind_of = str.lastIndexOf('!')
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len_minus_one = str.length - 1
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//
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//the case where '!' doesn't exist or not at the end
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if (last_ind_of == -1 || last_ind_of < len_minus_one) {
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return str
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} else { // this else only covers when str is ended with '!'
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//console.log(str + " () " + str.substr(0, len_minus_one))
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return str.substr(0, len_minus_one);
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}
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}

‎old/BEDataTest/2.js‎

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function vowelIndices(word) {
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let arr = [];
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for (i = 0; i < word.length; i++) {
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if (['a', 'e', 'i', 'o', 'u'].indexOf(word.charAt(i).toLowerCase()) !== -1) {
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arr.push(i + 1) // as indexed from [1..n]
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}
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}
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return arr
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}
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///*
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console.log(vowelIndices("aeioU"))
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console.log(vowelIndices("Mmmm"))
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console.log(vowelIndices("Apple"))
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console.log(vowelIndices("Super"))
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console.log(vowelIndices("Orange"))
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console.log(vowelIndices("supercalifragilisticexpialidocious"))
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//*/

‎old/BEDataTest/3.2.js‎

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var bananas = function(s) {
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console.log(s)
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recursive(s, "banana", "", []);
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}
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function recursive(s, ban, rslt_str, rslt_arr) {
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if (ban.length == 2) {
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console.log(rslt_str)
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return;
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}
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/*
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if (rslt_str.length == s_len && ban.length == 0) {
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rslt_arr.push(rslt_str);
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}
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*/
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for (i = 0; i < ban.length; i++) {
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for (j = 0; j < s.length; j++) {
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if (ban[i] == s[j]) {
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rslt_str += ban[i];
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console.log("if: " + s.substr(j + 1, s.length), ban.substr(i + 1, ban.length), rslt_str);
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recursive(s.substr(j + 1, s.length), ban.substr(i + 1, ban.length), rslt_str, rslt_arr)
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} else {
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rslt_str += "-";
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console.log("else: " + s.substr(j + 1, s.length), ban.substr(i + 1, ban.length), rslt_str);
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recursive(s.substr(j + 1, s.length), ban.substr(i + 1, ban.length), rslt_str, rslt_arr)
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}
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}
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}
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}
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bananas("bbananana");

‎old/BEDataTest/3.js‎

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var bananas = function(s) {
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// Your code here!
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let possible_comb = []
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let len_ban = "banana".length; // could be set manually to 6; as it is static
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let len_s = s.length; // later to be used many times, so stored in a vrble
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//
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for (i = 0; i < "banana".length; i++) {
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possible_comb.push(new Array(len_s).fill(0));
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count = 1;
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for (j = i; j <= len_s - (len_ban - i); j++) {
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if ("banana".charAt(i) == s.charAt(j)) {
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"banana".charAt(i) == s.charAt(j)
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possible_comb[i][j] = count++
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}
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}
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}
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let result_arr = []
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let comb_ind = len_ban - 1; // node 3.js
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console.log(comb_ind)
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//
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while (comb_ind >= 0) {
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let result_str;
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for (i = 0; i < len_ban; i++) {
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result_str = "";
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if (comb_ind == i) {
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console.log(i + " :if: " + j + " : " + result_str)
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for (j = i; j <= len_s - (len_ban - i); j++) {
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if (possible_comb[i][j] > 0) {
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result_str += "banana".charAt(i)
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possible_comb[i][j] = 0;
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console.log(i + " :if: " + j + " : " + result_str)
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break;
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}
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}
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} else if (possible_comb[i][j] > 0) {
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result_str += "banana".charAt(i)
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console.log(i + " :eif: " + j + " : " + result_str)
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} else {
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result_str += "-"
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console.log(i + " :else: " + j + " : " + result_str)
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}
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}
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comb_ind--;
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console.log(comb_ind)
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result_arr.push(result_str)
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}
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console.log(result_arr)
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return possible_comb
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}
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bananas("bbananana");

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