---
id: 5a23c84252665b21eecc8029
title: ストラドリングチェッカーボード
challengeType: 5
forumTopicId: 302325
dashedName: straddling-checkerboard
---

# --description--

[ストラドリングチェッカーボード](https://en.wikipedia.org/wiki/Straddling_checkerboard) メソッドを使用して、メッセージの暗号化と復号を行う関数を実装します。 関数はパラメータとして文字列と配列を取ります。 この配列にはチェッカーボードの3行を表す3つの文字列が含まれます。 出力は一連の 10 進数になります。 数字は各桁の前にエスケープ文字を挿入し、次に暗号化されていない桁を組み込んで暗号化する必要があります。 復号の場合は逆にします。

# --hints--

`straddle` は関数とします。

```js
assert(typeof straddle == 'function');
```

`straddle("One night-it was on the twentieth of March, 1888-I was returning.",["ESTONIA  R", "BCDFGHJKLM", "PQUVWXYZ./"])` は文字列を返す必要があります。

```js
assert(
  typeof straddle(
    'One night-it was on the twentieth of March, 1888-I was returning.',
    ['ESTONIA  R', 'BCDFGHJKLM', 'PQUVWXYZ./']
  ) == 'string'
);
```

`straddle("One night-it was on the twentieth of March, 1888-I was returning.",["ESTONIA  R", "BCDFGHJKLM", "PQUVWXYZ./"])` は `"34045747525284613427502840425027537379697175891898898898584619028294547488"` を返す必要があります。

```js
assert.equal(
  straddle(
    'One night-it was on the twentieth of March, 1888-I was returning.',
    ['ESTONIA  R', 'BCDFGHJKLM', 'PQUVWXYZ./']
  ),
  '34045747525284613427502840425027537379697175891898898898584619028294547488'
);
```

`straddle("One night-it was on the twentieth of March, 1888-I was returning",["HOL MES RT", "ABCDFGIJKN", "PQUVWXYZ./"])` は `"139539363509369743061399059745399365901344308320791798798798367430685972839363935"` を返す必要があります。

```js
assert.equal(
  straddle('One night-it was on the twentieth of March, 1888-I was returning', [
    'HOL MES RT',
    'ABCDFGIJKN',
    'PQUVWXYZ./'
  ]),
  '139539363509369743061399059745399365901344308320791798798798367430685972839363935'
);
```

`straddle("Thecheckerboardcakerecipespecifies3largeeggsand2.25cupsofflour.",["ET AON RIS", "BCDFGHJKLM", "PQ/UVWXYZ."])` は `"125021250212707204372221327070218600960021823809623283724002424935226226962262521636094232328463769"` を返す必要があります。

```js
assert.equal(
  straddle('Thecheckerboardcakerecipespecifies3largeeggsand2.25cupsofflour.', [
    'ET AON RIS',
    'BCDFGHJKLM',
    'PQ/UVWXYZ.'
  ]),
  '125021250212707204372221327070218600960021823809623283724002424935226226962262521636094232328463769'
);
```

`unstraddle` は関数とします。

```js
assert(typeof unstraddle == 'function');
```

`unstraddle("34045747525284613427502840425027537379697175891898898898584619028294547488",["ESTONIA  R", "BCDFGHJKLM", "PQUVWXYZ./"])` は文字列を返す必要があります。

```js
assert(
  typeof unstraddle(
    '34045747525284613427502840425027537379697175891898898898584619028294547488',
    ['ESTONIA  R', 'BCDFGHJKLM', 'PQUVWXYZ./']
  ) == 'string'
);
```

`unstraddle("34045747525284613427502840425027537379697175891898898898584619028294547488",["ESTONIA  R", "BCDFGHJKLM", "PQUVWXYZ./"])` は `"ONENIGHTITWASONTHETWENTIETHOFMARCH1888IWASRETURNING."` を返す必要があります。

```js
assert.equal(
  unstraddle(
    '34045747525284613427502840425027537379697175891898898898584619028294547488',
    ['ESTONIA  R', 'BCDFGHJKLM', 'PQUVWXYZ./']
  ),
  'ONENIGHTITWASONTHETWENTIETHOFMARCH1888IWASRETURNING.'
);
```

`unstraddle("139539363509369743061399059745399365901344308320791798798798367430685972839363935",["HOL MES RT", "ABCDFGIJKN", "PQUVWXYZ./"])` は `"ONENIGHTITWASONTHETWENTIETHOFMARCH1888IWASRETURNING"` を返す必要があります。

```js
assert.equal(
  unstraddle(
    '139539363509369743061399059745399365901344308320791798798798367430685972839363935',
    ['HOL MES RT', 'ABCDFGIJKN', 'PQUVWXYZ./']
  ),
  'ONENIGHTITWASONTHETWENTIETHOFMARCH1888IWASRETURNING'
);
```

`unstraddle("125021250212707204372221327070218600960021823809623283724002424935226226962262521636094232328463769",["ET AON RIS", "BCDFGHJKLM", "PQ/UVWXYZ."])` は `"THECHECKERBOARDCAKERECIPESPECIFIES3LARGEEGGSAND2.25CUPSOFFLOUR."` を返す必要があります。

```js
assert.equal(
  unstraddle(
    '125021250212707204372221327070218600960021823809623283724002424935226226962262521636094232328463769',
    ['ET AON RIS', 'BCDFGHJKLM', 'PQ/UVWXYZ.']
  ),
  'THECHECKERBOARDCAKERECIPESPECIFIES3LARGEEGGSAND2.25CUPSOFFLOUR.'
);
```

# --seed--

## --seed-contents--

```js
function straddle(message, alphabet) {

}

function unstraddle(message, alphabet) {

}
```

# --solutions--

```js
function straddle(message, alphabet) {
  var prefixes = new Array(
    '',
    alphabet[0].indexOf(' '),
    alphabet[0].lastIndexOf(' ')
  );

  var out = '';
  message = message.toUpperCase();
  message = message.replace(/([0-9])/g, '/$1'); // dumb way to escape numbers
  for (var i = 0; i < message.length; i++) {
    var chr = message[i];
    if (chr == ' ') continue;
    for (var j = 0; j < 3; j++) {
      var k = alphabet[j].indexOf(chr);
      if (k < 0) continue;
      out += prefixes[j].toString() + k;
    }
    if (chr == '/') out += message[++i];
  }
  return out;
}
function unstraddle(message, alphabet) {
  var prefixes = new Array(
    '',
    alphabet[0].indexOf(' '),
    alphabet[0].lastIndexOf(' ')
  );
  var out = '';
  var n, o;
  for (var i = 0; i < message.length; i++) {
    n = message[i] * 1;
    switch (n) {
      case prefixes[1]:
        o = alphabet[1][message[++i]];
        break;
      case prefixes[2]:
        o = alphabet[2][message[++i]];
        break;
      default:
        o = alphabet[0][n];
    }
    o == '/' ? (out += message[++i]) : (out += o);
  }
  return out;
}
```