２次元配列を左に90°回転させるサンプル

gistfile1.txt

const assert = require('assert');

const arr = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
const answer = [[3, 6, 9], [2, 5, 8], [1, 4, 7]];
const wrongAnswer = [[4, 6, 9], [2, 5, 8], [1, 4, 7]];

const rotate = b => {
  const transpose = a => a[0].map((_, c) => a.map(r => r[c]));
  return transpose(b).reverse();
};

assert.deepStrictEqual(answer, rotate(arr), '正しく処理されていない');
assert.notDeepStrictEqual(wrongAnswer, rotate(arr), '正しく処理されていない');