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@aminnairi
Created Feb 4, 2022
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// For these excercises :
// - Only use recursion (or direct recursion)
// - Array.prototype methods are prohibited
// - for, while & do while loops are prohibited
// - Array.prototype.length is accepted
/**
* @description Update every item of an array
* @param {<Type>(item: Type) => Type} update A function that will update one item
* @param {Array<Type>} items An array of items to update
* @return {Array<Type>} An array of all of the items updated
* @example
* const increment = value => value + 1;
* const items = [1, 2, 3, 4, 5];
* map(increment, items); // [increment(2), increment(3), increment(4), increment(5), increment(6)]
* map(incrment, []); // []
*/
export const map = (update, items) => {
if (items.length === 0) {
return [];
}
const [item, ...remainingItems] = items;
return [update(item), ...update(update, remainingItems)];
};
/**
* @description Remove all items that do not satisfy a condition
* @param {<Type>(item: Type) => boolean} accepted A function that will take an item and check if it should be accepted
* @param {Array<Type>} items An array of items
* @return {Array<Type>} An array of all of the items accepted
* @example
* const even = value => value % 2 === 0;
* const items = [1, 2, 3, 4, 5];
* only(even, items); // [2, 4]
*/
export const only = (accepted, items) => {
if (items.length === 0) {
return [];
}
const [item, ...remainingItems] = items;
if (accepted(item)) {
return [item, ...only(accepted, remainingItems)];
}
return only(accepted, remainingItems);
};
/**
* @description Remove all items that satisfy a condition
* @param {<Type>(item: Type) => boolean} accepted A function that will take an item and check if it should be removed
* @param {Array<Type>} items An array of items
* @return {Array<Type>} An array of all of the items accepted
* @example
* const even = value => value % 2 === 0;
* const items = [1, 2, 3, 4, 5];
* except(even, items); // [1, 3, 5]
*/
export const except = (accepted, items) => {
if (items.length === 0) {
return [];
}
const [item, ...remainingItems] = items;
if (accepted(item)) {
return except(accepted, remainingItems);
}
return [item, ...except(accepted, remainingItems)];
};
/**
* @description Check if at least one of the items satisfy a condition
* @param {<Type>(item: Type) => boolean} accepted A function that will take an item and check if it is accepted
* @param {Array<Type>} items An array of items
* @return {boolean} True if at least one of the items satisfy a condition, false otherwise
* @example
* const even = value => value % 2 === 0;
* const highNumber = value => value > 10;
* const items = [1, 2, 3, 4, 5];
* some(even, items); // true
* some(highNumber, items); // false
*/
export const some = (accepted, items) => {
if (items.length === 0) {
return false;
}
const [item, ...remainingItems] = items;
if (accepted(item)) {
return true;
}
return some(accepted, remainingItems);
};
/**
* @description Check if all of the items satisfy a condition
* @param {<Type>(item: Type) => boolean} accepted A function that will take an item and check if it is accepted
* @param {Array<Type>} items An array of items
* @return {boolean} True if all of the items satisfy a condition, false otherwise
* @example
* const even = value => value % 2 === 0;
* const lowNumber = value => value < 10;
* const items = [1, 2, 3, 4, 5];
* every(even, items); // false
* every(lowNumber, items); // true
*/
export const every = (accepted, items) => {
if (items.length === 0) {
return true;
}
const [item, ...remainingItems] = items;
if (accepted(item)) {
return every(accepted, remainingItems);
}
return false;
};
/**
* @description Attempt at finding an element that satisfy a condition
* @param {<Type>(item: Type) => boolean} found A function that will take an item and check if it is found
* @param {Array<Type>} items An array of items to search for
* @return {Type | null} The item if found, or null if not
* @example
* const even = value => value % 2 === 0;
* const highNumber = value => value > 10;
* const items = [1, 3, 4, 5, 7];
* find(even, items); // 4
* find(highNumber, items); // null
*/
export const find = (found, items) => {
if (items.length === 0) {
return null;
}
const [item, ...remainingItems] = items;
if (found(item)) {
return item;
}
return find(found, remainingItems);
};
/**
* @description Attempt at finding the index of an element that satisfy a condition
* @param {<Type>(item: Type) => boolean} found A function that will take an item and check if it is found
* @param {Array<Type>} items An array of items to search for
* @return {number} The index of the found item, or -1
* @example
* const even = value => value % 2 === 0;
* const highNumber = value => value > 10;
* const items = [1, 3, 4, 5, 7];
* findIndex(even, items); // 2
* findIndex(highNumber, items); // -1
*/
export const findIndex = (found, items, index = 0) => {
if (items.length === 0) {
return -1;
}
const [item, ...remainingItems] = items;
if (found(item)) {
return index; // 0
}
return findIndex(found, remainingItems, index + 1);
};
/**
* @description Transform an array of items into something else
* @param {<AnotherType>(accumulator: AnotherType, item: Type) => AnotherType} reducer A transformer function that has access to the previous accumulation and the current iterated item
* @param {AnotherType} state The initial value that the reducer function should take as accumulation
* @param {Array<Type>} items An array of elements
* @return {AnotherType} The transformation of the array into something else
* @example
* const initialOccurrences = {};
* const computeOccurrences = (previousOccurrences, letter) => letter in occurrences ? ({...occurrences, [letter]: occurrences[letter] + 1}) : ({...occurrences, [letter]: 1});
* fold(computeOccurrences, initialOccurrences, ["b", "a", "b", "c", "b", "a", "b"]); // {"a": 2, "b": 3, "c": 1}
*/
export const fold = (reducer, state, items) => {
if (items.length === 0) {
return state;
}
const [item, ...remainingItems] = items;
return fold(reducer, reducer(state, item), remainingItems);
};
/**
* @summary Niveau Avancé
* @description Implémenter toutes les fonctions listées à l'URL ci-dessous sauf celle déjà faites ci-dessus et les fonctions qui acceptent/renvoient un Maybe
* @see https://package.elm-lang.org/packages/elm/core/latest/List
*/
/**
* @summary Niveau Expert
* @description Implémenter toutes les fonctions listées à l'URL ci-dessous sauf celle déjà faites ci-dessus et les fonctions qui acceptent/renvoient un Maybe
* @see https://package.elm-lang.org/packages/elm-community/list-extra/latest/List-Extra
*/
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