permute integer range [0, 56800235583]

shortener_b36d7.js

const digits = "0123456789abcdefghijklmnopqrstuvwxyz";
const digitsReverse = (function(){
  var arr = digits.split('');
  var table = {};
  for(var i=0; i<arr.length; i++) table[arr[i]] = i;
  return table;
})();
const dim = 7;
const modulo = 36;
const shift = [11, 21, 21, 23, 4, 24, 1];
const forward = [
  [11, 0, 7, 19, 19, 5, 23],
  [31, 4, 30, 5, 18, 22, 31],
  [6, 4, 13, 26, 12, 30, 32],
  [11, 5, 11, 20, 25, 30, 14],
  [33, 28, 2, 8, 20, 5, 18],
  [17, 20, 16, 11, 21, 2, 10],
  [30, 23, 27, 23, 29, 10, 14]
];
const backward = [
  [7, 25, 25, 29, 27, 15, 33],
  [25, 23, 18, 9, 11, 34, 20],
  [14, 26, 3, 16, 20, 26, 4],
  [11, 9, 31, 18, 31, 1, 10],
  [22, 12, 12, 17, 20, 21, 9],
  [5, 33, 17, 33, 26, 25, 9],
  [22, 1, 34, 25, 24, 2, 17]
];

function encode(id) {
  // O(dim)
  var arr = new Array(dim);
  for (let i=0; i<dim; i++){
    arr[i] = id % modulo;
    id = Math.floor(id/modulo);
  }
  // O(dim^2)
  var res = shift.concat();
  for(let i=0; i<dim; i++){
    for(let j=0; j<dim; j++){
      res[i] += forward[i][j] * arr[j];
    }
  }
  return res.map(i => digits[i%modulo]).join('');
}

function decode(hash) {
  // assert( hash.length == dim )

  // O(dim)
  var arr = new Array(dim);
  for(let i=0; i<dim; i++){
    var c = hash[i];
    arr[i] = digitsReverse[c] + modulo - shift[i];
  }

  // O(dim^2)
  var ans = 0;
  var base = 1;
  for(let i=0; i<dim; i++){
    var t = 0;
    for(let j=0; j<dim; j++){
      t += backward[i][j] * arr[j];
    }
    ans += (t%modulo) * base;
    base *= modulo;
  }

  return ans;
}

module.exports = {
  encode: encode,
  decode: decode
};