javascript - run-length-encoding

javascript/run-length-encoding/README.md

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+# Run Length Encoding
+
+Implement run-length encoding and decoding.
+
+Run-length encoding (RLE) is a simple form of data compression, where runs
+(consecutive data elements) are replaced by just one data value and count.
+
+For example we can represent the original 53 characters with only 13.
+
+```text
+"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"  ->  "12WB12W3B24WB"
+```
+
+RLE allows the original data to be perfectly reconstructed from
+the compressed data, which makes it a lossless data compression.
+
+```text
+"AABCCCDEEEE"  ->  "2AB3CD4E"  ->  "AABCCCDEEEE"
+```
+
+For simplicity, you can assume that the unencoded string will only contain
+the letters A through Z (either lower or upper case) and whitespace. This way
+data to be encoded will never contain any numbers and numbers inside data to
+be decoded always represent the count for the following character.
+
+## 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`.
+
+
+## Source
+
+Wikipedia [https://en.wikipedia.org/wiki/Run-length_encoding](https://en.wikipedia.org/wiki/Run-length_encoding)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

javascript/run-length-encoding/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/run-length-encoding/run-length-encoding.js

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+exports.encode = function (string) {
+  let counter = 1;
+  let output = '';
+  for (let i = 0; i < string.length; i++) {
+    if (string[i] == string[i + 1]) {
+      counter++;
+    } else {
+      if (counter > 1) {
+        output += counter;
+      }
+      output += string[i];
+      counter = 1;
+    }
+  }
+  return output;
+};
+
+exports.decode = function (string) {
+  let output = '';
+  let number = '';
+  for (let i = 0; i < string.length; i++) {
+    if (!isNaN(parseInt(string[i]))) {
+      number += string[i];
+    } else {
+      const count = isNaN(parseInt(number)) ? 1 : parseInt(number);
+      output += string[i].repeat(count);
+      number = '';
+    }
+  }
+  return output;
+};

javascript/run-length-encoding/run-length-encoding.spec.js

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+import { encode, decode } from './run-length-encoding';
+
+describe('run-length encode a string', () => {
+  test('encode empty string', () => {
+    expect(encode('')).toEqual('');
+  });
+
+  test('single characters only are encoded without count', () => {
+    expect(encode('XYZ')).toEqual('XYZ');
+  });
+
+  test('encode string with no single characters', () => {
+    expect(encode('AABBBCCCC')).toEqual('2A3B4C');
+  });
+
+  test('encode string with single characters mixed with repeated characters', () => {
+    expect(encode('WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB')).toEqual('12WB12W3B24WB');
+  });
+
+  test('encode string with multiple whitespaces', () => {
+    expect(encode('  hsqq qww  ')).toEqual('2 hs2q q2w2 ');
+  });
+
+  test('encode string with lowercase characters', () => {
+    expect(encode('aabbbcccc')).toEqual('2a3b4c');
+  });
+});
+
+describe('run-length decode a string', () => {
+  test('decode empty string', () => {
+    expect(decode('')).toEqual('');
+  });
+
+  test('decode string with single characters only', () => {
+    expect(decode('XYZ')).toEqual('XYZ');
+  });
+
+  test('decode string with no single characters', () => {
+    expect(decode('2A3B4C')).toEqual('AABBBCCCC');
+  });
+
+  test('decode string with single characters mixed with repeated characters', () => {
+    expect(decode('12WB12W3B24WB')).toEqual('WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB');
+  });
+
+  test('decode string with multiple whitespaces', () => {
+    expect(decode('2 hs2q q2w2 ')).toEqual('  hsqq qww  ');
+  });
+
+  test('decode string with lowercase characters', () => {
+    expect(decode('2a3b4c')).toEqual('aabbbcccc');
+  });
+});
+
+describe('run-length encode and then decode', () => {
+  test('encode followed by decode gives original string', () => {
+    expect(decode(encode('zzz ZZ  zZ'))).toEqual('zzz ZZ  zZ');
+  });
+});