javascript - zipper

javascript/zipper/README.md

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+# Zipper
+
+Creating a zipper for a binary tree.
+
+[Zippers](https://en.wikipedia.org/wiki/Zipper_%28data_structure%29) are
+a purely functional way of navigating within a data structure and
+manipulating it.  They essentially contain a data structure and a
+pointer into that data structure (called the focus).
+
+For example given a rose tree (where each node contains a value and a
+list of child nodes) a zipper might support these operations:
+
+- `from_tree` (get a zipper out of a rose tree, the focus is on the root node)
+- `to_tree` (get the rose tree out of the zipper)
+- `value` (get the value of the focus node)
+- `prev` (move the focus to the previous child of the same parent,
+  returns a new zipper)
+- `next` (move the focus to the next child of the same parent, returns a
+  new zipper)
+- `up` (move the focus to the parent, returns a new zipper)
+- `set_value` (set the value of the focus node, returns a new zipper)
+- `insert_before` (insert a new subtree before the focus node, it
+  becomes the `prev` of the focus node, returns a new zipper)
+- `insert_after` (insert a new subtree after the focus node, it becomes
+  the `next` of the focus node, returns a new zipper)
+- `delete` (removes the focus node and all subtrees, focus moves to the
+  `next` node if possible otherwise to the `prev` node if possible,
+  otherwise to the parent node, returns a new zipper)
+
+## Setup
+
+Go through the setup instructions for Javascript to
+install the necessary dependencies:
+
+[https://exercism.io/tracks/javascript/installation](https://exercism.io/tracks/javascript/installation)
+
+## Requirements
+
+Install assignment dependencies:
+
+```bash
+$ npm install
+```
+
+## Making the test suite pass
+
+Execute the tests with:
+
+```bash
+$ npm test
+```
+
+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 `xtest` to `test`.
+
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

javascript/zipper/package.json

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+{
+  "name": "exercism-javascript",
+  "version": "0.0.0",
+  "description": "Exercism exercises in Javascript.",
+  "author": "Katrina Owen",
+  "private": true,
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/exercism/javascript"
+  },
+  "devDependencies": {
+    "babel-jest": "^21.2.0",
+    "babel-plugin-transform-builtin-extend": "^1.1.2",
+    "babel-preset-env": "^1.4.0",
+    "eslint": "^3.19.0",
+    "eslint-config-airbnb": "^15.0.1",
+    "eslint-plugin-import": "^2.2.0",
+    "eslint-plugin-jsx-a11y": "^5.0.1",
+    "eslint-plugin-react": "^7.0.1",
+    "jest": "^21.2.1"
+  },
+  "jest": {
+    "modulePathIgnorePatterns": [
+      "package.json"
+    ]
+  },
+  "babel": {
+    "presets": [
+      [
+        "env",
+        {
+          "targets": [
+            {
+              "node": "current"
+            }
+          ]
+        }
+      ]
+    ],
+    "plugins": [
+      [
+        "babel-plugin-transform-builtin-extend",
+        {
+          "globals": [
+            "Error"
+          ]
+        }
+      ],
+      [
+        "transform-regenerator"
+      ]
+    ]
+  },
+  "scripts": {
+    "test": "jest --no-cache ./*",
+    "watch": "jest --no-cache --watch ./*",
+    "lint": "eslint .",
+    "lint-test": "eslint . && jest --no-cache ./* "
+  },
+  "eslintConfig": {
+    "parserOptions": {
+      "ecmaVersion": 6,
+      "sourceType": "module"
+    },
+    "env": {
+      "es6": true,
+      "node": true,
+      "jest": true
+    },
+    "extends": "airbnb",
+    "rules": {
+      "import/no-unresolved": "off",
+      "import/extensions": "off"
+    }
+  },
+  "licenses": [
+    "MIT"
+  ],
+  "dependencies": {}
+}

javascript/zipper/zipper.js

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+class Zipper {
+  constructor(tree) {
+    // quick hack for deep object clone.
+    this.tree = JSON.parse(JSON.stringify(tree));
+    this.focus = [];
+  }
+
+  static fromTree(tree) {
+    return new Zipper(tree);
+  }
+
+  toTree() {
+    return this.tree;
+  }
+
+  left() {
+    const subtree = this.getSubtree();
+    if (subtree.left) {
+      this.focus.push('left');
+      return this;
+    }
+    return null;
+  }
+
+  right() {
+    const subtree = this.getSubtree();
+    if (subtree.right) {
+      this.focus.push('right');
+      return this;
+    }
+    return null;
+  }
+
+  value() {
+    const subtree = this.getSubtree();
+    return subtree.value;
+  }
+
+  up() {
+    if (this.focus.length > 0) {
+      this.focus.pop();
+      return this;
+    }
+    return null;
+  }
+
+  setValue(value) {
+    const subtree = this.getSubtree();
+    subtree.value = value;
+    return this;
+  }
+
+  setLeft(left) {
+    const subtree = this.getSubtree();
+    subtree.left = left;
+    return this;
+  }
+
+  setRight(right) {
+    const subtree = this.getSubtree();
+    subtree.right = right;
+    return this;
+  }
+
+  getSubtree(subtree = null, step = 0) {
+    if (step == 0) {
+      subtree = this.tree;
+    }
+
+    if (step == this.focus.length) {
+      return subtree;
+    }
+
+    return this.getSubtree(subtree[this.focus[step]], step + 1);
+  }
+}
+
+export default Zipper;

javascript/zipper/zipper.spec.js

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+import Zipper from './zipper';
+
+// Tests adapted from `problem-specifications/zipper/canonical-data.json` @ v1.0.0
+
+function bt(value, left, right) {
+  return {
+    value,
+    left,
+    right,
+  };
+}
+
+function leaf(value) {
+  return bt(value, null, null);
+}
+
+describe('Zipper', () => {
+  const t1 = bt(1, bt(2, null, leaf(3)), leaf(4));
+  const t2 = bt(1, bt(5, null, leaf(3)), leaf(4));
+  const t3 = bt(1, bt(2, leaf(5), leaf(3)), leaf(4));
+  const t4 = bt(1, leaf(2), leaf(4));
+  const t5 = bt(1, bt(2, null, leaf(3)), bt(6, leaf(7), leaf(8)));
+  const t6 = bt(1, bt(2, null, leaf(5)), leaf(4));
+  let zipper;
+
+  beforeEach(() => {
+    zipper = Zipper.fromTree(t1);
+  });
+
+  test('data is retained', () => {
+    expect(zipper.toTree()).toEqual(t1);
+  });
+
+  test('left, right and value', () => {
+    expect(zipper.left().right().value()).toEqual(3);
+  });
+
+  test('dead end', () => {
+    expect(zipper.left().left()).toBe(null);
+  });
+
+  test('tree from deep focus', () => {
+    expect(zipper.left().right().toTree()).toEqual(t1);
+  });
+
+  test('traversing up from top', () => {
+    expect(zipper.up()).toEqual(null);
+  });
+
+  test('left, right and up', () => {
+    expect(zipper.left().up().right().up().left().right().value()).toEqual(3);
+  });
+
+  test('setValue', () => {
+    expect(zipper.left().setValue(5).toTree()).toEqual(t2);
+  });
+
+  test('setValue after traversing up', () => {
+    expect(zipper.left().right().up().setValue(5).toTree()).toEqual(t2);
+  });
+
+  test('setLeft with leaf', () => {
+    expect(zipper.left().setLeft(leaf(5)).toTree()).toEqual(t3);
+  });
+
+  test('setRight with null', () => {
+    expect(zipper.left().setRight(null).toTree()).toEqual(t4);
+  });
+
+  test('setRight with subtree', () => {
+    expect(zipper.setRight(bt(6, leaf(7), leaf(8))).toTree()).toEqual(t5);
+  });
+
+  test('setValue on deep focus', () => {
+    expect(zipper.left().right().setValue(5).toTree()).toEqual(t6);
+  });
+});