Linked list

typescript/linked-list/.eslintignore

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+!.meta
+
+# Protected or generated
+.git
+.vscode
+
+# When using npm
+node_modules/*
+
+# Configuration files
+.eslintrc.cjs
+babel.config.cjs
+jest.config.cjs

typescript/linked-list/.eslintrc.cjs

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+module.exports = {
+  root: true,
+  parserOptions: {
+    tsconfigRootDir: __dirname,
+    project: ['./tsconfig.json'],
+  },
+  overrides: [
+    // Student provided files
+    {
+      files: ['*.ts'],
+      excludedFiles: ['.meta/proof.ci.ts', '.meta/exemplar.ts', '*.test.ts'],
+      extends: '@exercism/eslint-config-typescript',
+    },
+    // Exercism given tests
+    {
+      files: ['*.test.ts'],
+      excludedFiles: ['custom.test.ts'],
+      env: {
+        jest: true,
+      },
+      extends: '@exercism/eslint-config-typescript/maintainers',
+    },
+    // Student provided tests
+    {
+      files: ['custom.test.ts'],
+      env: {
+        jest: true,
+      },
+      extends: '@exercism/eslint-config-typescript',
+    },
+    // Exercism provided files
+    {
+      files: ['.meta/proof.ci.ts', '.meta/exemplar.ts', '*.test.ts'],
+      excludedFiles: ['custom.test.ts'],
+      extends: '@exercism/eslint-config-typescript/maintainers',
+      rules: {
+        "@typescript-eslint/semi": 0,
+      },
+    },
+  ],
+}

typescript/linked-list/.exercism/config.json

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+{
+  "blurb": "Implement a doubly linked list",
+  "authors": ["jspengeman"],
+  "contributors": ["masters3d", "SleeplessByte"],
+  "files": {
+    "solution": ["linked-list.ts"],
+    "test": ["linked-list.test.ts"],
+    "example": [".meta/proof.ci.ts"]
+  },
+  "source": "Classic computer science topic"
+}

typescript/linked-list/.exercism/metadata.json

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+{"track":"typescript","exercise":"linked-list","id":"3f131a779e684267985af3d611b37402","url":"https://exercism.org/tracks/typescript/exercises/linked-list","handle":"briemens","is_requester":true,"auto_approve":false}

typescript/linked-list/HELP.md

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+# Help
+
+## Running the tests
+
+Execute the tests with:
+
+```bash
+$ yarn test
+```
+
+## Skipped tests
+
+In the test suites all tests but the first have been skipped.
+
+Once you get a test passing, you can enable the next one by changing `xit` to
+`it`.
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit linked-list.ts` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [TypeScript track's documentation](https://exercism.org/docs/tracks/typescript)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+To get help if you're having trouble, you can use one of the following resources:
+
+- [TypeScript QuickStart](https://www.typescriptlang.org/docs/handbook/release-notes/overview.html)
+- [ECMAScript 2015 Language Specification](https://www.ecma-international.org/wp-content/uploads/ECMA-262_6th_edition_june_2015.pdf) (pdf)
+- [Mozilla JavaScript Reference](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference)
+- [/r/typescript](https://www.reddit.com/r/typescript) is the TypeScript subreddit.
+- [StackOverflow](https://stackoverflow.com/questions/tagged/typescript) can be used to search for your problem and see if it has been answered already. You can also ask and answer questions.

typescript/linked-list/README.md

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+# Linked List
+
+Welcome to Linked List on Exercism's TypeScript Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+Implement a doubly linked list.
+
+Like an array, a linked list is a simple linear data structure. Several
+common data types can be implemented using linked lists, like queues,
+stacks, and associative arrays.
+
+A linked list is a collection of data elements called _nodes_. In a
+_singly linked list_ each node holds a value and a link to the next node.
+In a _doubly linked list_ each node also holds a link to the previous
+node.
+
+You will write an implementation of a doubly linked list. Implement a
+Node to hold a value and pointers to the next and previous nodes. Then
+implement a List which holds references to the first and last node and
+offers an array-like interface for adding and removing items:
+
+- `push` (_insert value at back_);
+- `pop` (_remove value at back_);
+- `shift` (_remove value at front_).
+- `unshift` (_insert value at front_);
+
+To keep your implementation simple, the tests will not cover error
+conditions. Specifically: `pop` or `shift` will never be called on an
+empty list.
+
+If you want to know more about linked lists, check [Wikipedia](https://en.wikipedia.org/wiki/Linked_list).
+
+## Source
+
+### Created by
+
+- @jspengeman
+
+### Contributed to by
+
+- @masters3d
+- @SleeplessByte
+
+### Based on
+
+Classic computer science topic

typescript/linked-list/babel.config.cjs

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+module.exports = {
+  presets: ['@exercism/babel-preset-typescript'],
+  plugins: [],
+}

typescript/linked-list/jest.config.cjs

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+module.exports = {
+  verbose: true,
+  projects: ['<rootDir>'],
+  testMatch: [
+    '**/__tests__/**/*.[jt]s?(x)',
+    '**/test/**/*.[jt]s?(x)',
+    '**/?(*.)+(spec|test).[jt]s?(x)',
+  ],
+  testPathIgnorePatterns: [
+    '/(?:production_)?node_modules/',
+    '.d.ts$',
+    '<rootDir>/test/fixtures',
+    '<rootDir>/test/helpers',
+    '__mocks__',
+  ],
+  transform: {
+    '^.+\\.[jt]sx?$': 'babel-jest',
+  },
+}

typescript/linked-list/linked-list.test.ts

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+import { LinkedList } from "./linked-list";
+
+describe("LinkedList", () => {
+  it("add/extract elements to the end of the list with push/pop", () => {
+    const list = new LinkedList<number>();
+    list.push(10);
+    list.push(20);
+    expect(list.pop()).toBe(20);
+    expect(list.pop()).toBe(10);
+  });
+
+  it("extract elements from the beginning of the list with shift", () => {
+    const list = new LinkedList<number>();
+    list.push(10);
+    list.push(20);
+    expect(list.shift()).toBe(10);
+    expect(list.shift()).toBe(20);
+  });
+
+  it("add/extract elements from the beginning of the list with unshift/shift", () => {
+    const list = new LinkedList<number>();
+    list.unshift(10);
+    list.unshift(20);
+    expect(list.shift()).toBe(20);
+    expect(list.shift()).toBe(10);
+  });
+
+  it("unshift/pop", () => {
+    const list = new LinkedList<number>();
+    list.unshift(10);
+    list.unshift(20);
+    expect(list.pop()).toBe(10);
+    expect(list.pop()).toBe(20);
+  });
+
+  it("example", () => {
+    const list = new LinkedList<number>();
+    list.push(10);
+    list.push(20);
+    expect(list.pop()).toBe(20);
+    list.push(30);
+    expect(list.shift()).toBe(10);
+    list.unshift(40);
+    list.push(50);
+    expect(list.shift()).toBe(40);
+    expect(list.pop()).toBe(50);
+    expect(list.shift()).toBe(30);
+  });
+
+  it("can count its elements", () => {
+    const list = new LinkedList<number>();
+    expect(list.count()).toBe(0);
+    list.push(10);
+    expect(list.count()).toBe(1);
+    list.push(20);
+    expect(list.count()).toBe(2);
+  });
+
+  it("sets head/tail after popping last element", () => {
+    const list = new LinkedList<number>();
+    list.push(10);
+    list.pop();
+    list.unshift(20);
+    expect(list.count()).toBe(1);
+    expect(list.pop()).toBe(20);
+  });
+
+  it("sets head/tail after shifting last element", () => {
+    const list = new LinkedList<number>();
+    list.unshift(10);
+    list.shift();
+    list.push(20);
+    expect(list.count()).toBe(1);
+    expect(list.shift()).toBe(20);
+  });
+
+  it("deletes the element with the specified value from the list", () => {
+    const list = new LinkedList<number>();
+    list.push(10);
+    list.push(20);
+    list.push(30);
+    list.delete(20);
+    expect(list.count()).toBe(2);
+    expect(list.pop()).toBe(30);
+    expect(list.shift()).toBe(10);
+  });
+
+  it("deletes the only element", () => {
+    const list = new LinkedList<number>();
+    list.push(10);
+    list.delete(10);
+    expect(list.count()).toBe(0);
+  });
+
+  it("delete does not modify the list if the element is not found", () => {
+    const list = new LinkedList<number>();
+    list.push(10);
+    list.delete(20);
+    expect(list.count()).toBe(1);
+  });
+});

typescript/linked-list/linked-list.ts

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+interface Node<TValue> {
+  previous?: Node<TValue>;
+  value: TValue;
+  next?: Node<TValue>;
+}
+
+const push = <TValue extends any>(
+  node: Node<TValue> | undefined,
+  value: TValue
+): Node<TValue> => {
+  if (!node) {
+    return { value };
+  }
+  if (node.next) {
+    push(node.next, value);
+    return node;
+  }
+  node.next = { previous: node, value };
+  return node;
+};
+
+const pop = <TValue extends any>(
+  node?: Node<TValue>
+): { node: Node<TValue> | undefined; value: TValue | undefined } => {
+  if (!node) {
+    return { node: undefined, value: undefined };
+  }
+  if (node.next) {
+    const { value } = pop(node.next);
+    return { node, value };
+  }
+  if (node.previous) {
+    node.previous.next = undefined;
+  }
+  return { node: undefined, value: node.value };
+};
+
+const shift = <TValue extends any>(
+  node?: Node<TValue>
+): { node: Node<TValue> | undefined; value: TValue | undefined } => {
+  if (!node) {
+    return { node: undefined, value: undefined };
+  }
+  if (node.next) {
+    node.next.previous = undefined;
+    return { node: node.next, value: node.value };
+  }
+  return { node: undefined, value: node.value };
+};
+
+const unshift = <TValue extends any>(
+  node: Node<TValue> | undefined,
+  value: TValue
+): Node<TValue> => {
+  if (!node) {
+    return { value };
+  }
+  const root = { value, next: node };
+  node.previous = root;
+  return root;
+};
+
+const count = <TValue extends any>(node: Node<TValue> | undefined): number => {
+  if (!node) {
+    return 0;
+  }
+  return 1 + count(node.next);
+};
+
+const del = <TValue extends any>(
+  node: Node<TValue> | undefined,
+  value: TValue
+): Node<TValue> | undefined => {
+  if (!node) {
+    return undefined;
+  }
+  if (node.next) {
+    del(node.next, value);
+  }
+  if (node.value === value) {
+    if (node.previous) {
+      node.previous.next = node.next;
+    }
+    if (node.next) {
+      node.next.previous = node.previous;
+    }
+    return undefined;
+  }
+  return node;
+};
+
+export class LinkedList<TElement> {
+  public node: Node<TElement> | undefined;
+  push(value: TElement): void {
+    this.node = push(this.node, value);
+  }
+  pop(): TElement | undefined {
+    const { node, value } = pop(this.node);
+    this.node = node;
+    return value;
+  }
+  shift(): TElement | undefined {
+    const { node, value } = shift(this.node);
+    this.node = node;
+    return value;
+  }
+  unshift(value: TElement): void {
+    this.node = unshift(this.node, value);
+  }
+  delete(element: TElement): void {
+    this.node = del(this.node, element);
+  }
+  count(): number {
+    return count(this.node);
+  }
+}

typescript/linked-list/package.json

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+{
+  "name": "@exercism/typescript-linked-list",
+  "version": "1.0.0",
+  "description": "Exercism exercises in Typescript.",
+  "private": true,
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/exercism/typescript"
+  },
+  "type": "module",
+  "engines": {
+    "node": "^14.13.1 || >=16.0.0"
+  },
+  "devDependencies": {
+    "@exercism/babel-preset-typescript": "^0.1.0",
+    "@exercism/eslint-config-typescript": "^0.4.1",
+    "@types/jest": "^27.4.0",
+    "@types/node": "^16.11.24",
+    "babel-jest": "^27.5.1",
+    "core-js": "^3.21.0",
+    "eslint": "^8.9.0",
+    "jest": "^27.5.1",
+    "typescript": "^4.5.4"
+  },
+  "scripts": {
+    "test": "yarn lint:types && jest --no-cache",
+    "lint": "yarn lint:types && yarn lint:ci",
+    "lint:types": "yarn tsc --noEmit -p .",
+    "lint:ci": "eslint . --ext .tsx,.ts"
+  }
+}

typescript/linked-list/tsconfig.json

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+{
+  "display": "Configuration for Exercism TypeScript Exercises",
+  "compilerOptions": {
+    // Allows you to use the newest syntax, and have access to console.log
+    // https://www.typescriptlang.org/tsconfig#lib
+    "lib": ["ESNEXT", "dom"],
+    // Make sure typescript is configured to output ESM
+    // https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c#how-can-i-make-my-typescript-project-output-esm
+    "module": "ES2020",
+    // Since this project is using babel, TypeScript may target something very
+    // high, and babel will make sure it runs on your local Node version.
+    // https://babeljs.io/docs/en/
+    "target": "ESNext", // ESLint doesn't support this yet: "es2022",
+
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+
+    // Because we'll be using babel: ensure that Babel can safely transpile
+    // files in the TypeScript project.
+    //
+    // https://babeljs.io/docs/en/babel-plugin-transform-typescript/#caveats
+    "isolatedModules": true
+  },
+  "include": ["*.ts", "*.tsx", ".meta/*.ts", ".meta/*.tsx"],
+  "exclude": ["node_modules"]
+}