Normalizing a board game notation

Question

I have a board game notation for the game of Hnefatafl which I need to rotate clockwise. In the game of Hnefatafl we use a 11x11 board with files from A to K and ranks numbered from 1 to 11. So, here are the first three moves from the notation:

"1.k8-i8 g7-j7; 2.k5-j5 h6-h9; 3.k7-k9 f8-c8;"

After the rotation the notation must be like this:

"1.h1-h3 g5-g2; 2.e1-e2 f4-i4; 3.g1-i1 h6-h9;"

How can I rotate the board and normalize the notation by using a JavaScript function?

"how can I in javascript"... you write a javascript function that does that. If you have tried that and gotten stuck somewhere, please include your code and doubts in your question. If you have not tried, now would be a great time to start. — teapot418, Mar 06 '23 at 16:56
Unless you show some of your own effort and ask a question different from "write this for me", your post is likely to be downvoted and closed. Some recommended reading while you wait: [Open letter to students with homework problems.](https://softwareengineering.meta.stackexchange.com/q/6166) — teapot418, Mar 06 '23 at 17:27

nullromo · Answer 1 · 2023-03-07T00:55:43.570

When you rotate the board, you can see that anything that used to be in file A is now in rank 11; anything that was in file K is now in rank 1, etc.

In general, take the rank letter's ordinal position and subtract it from 11.

old file	old file ascii value	subtract 97 (ordinal position)	new rank (11 - ordinal)
'a'	97	0	11
'b'	98	1	10
'c'	99	2	9
...	...	...	...
'k'	107	10	1

Likewise, the old ranks can get mapped in a similar way

old rank	new file
1	a
2	b
3	c
...
11	k

So if your coordinates are of the form:

{
    file: 'a',
    rank: 11,
}

then you can just transform them using a function like this:

const transform = (oldSpace) => {
    return {
        rank: 11 - (oldSpace.file.charCodeAt(0) - 97)
        file: String.fromCharCode(oldSpace.rank + 96)
    };
};

Then you can just transform them to the new coordinate system.

console.log(transform({ file: 'k', rank: 8 })); // => h1
console.log(transform({ file: 'i', rank: 8 })); // => h3
console.log(transform({ file: 'g', rank: 7 })); // => g5
console.log(transform({ file: 'j', rank: 7 })); // => g2

Sample implementation

const transform = (oldSpace) => {
    const match = oldSpace.match(/^(?<file>\w)(?<rank>\d+)$/);
    const file = String.fromCharCode(Number(match.groups.rank) + 96);
    const rank = 11 - (match.groups.file.charCodeAt(0) - 97);
    return `${rank}${file}`;
};

const parseTurn = (turn) => {
    const match = turn.match(
        /^(?<turnNumber>\d)\.(?<first>\w\d+)-(?<second>\w\d+) (?<third>\w\d+)-(?<fourth>\w\d+)$/,
    );
    return {
        turnNumber: parseInt(turn, 10),
        first: match.groups.first,
        second: match.groups.second,
        third: match.groups.third,
        fourth: match.groups.fourth,
    };
};

const transformGame = (input) => {
    return input
        .split(';')
        .filter((turn) => {
            return Boolean(turn);
        })
        .map((turn) => {
            return parseTurn(turn.trim());
        })
        .map((turn) => {
            return {
                turnNumber: turn.turnNumber,
                first: transform(turn.first),
                second: transform(turn.second),
                third: transform(turn.third),
                fourth: transform(turn.fourth),
            };
        })
        .map((turn) => {
            return `${turn.turnNumber}.${turn.first}-${turn.second} ${turn.third}-${turn.fourth};`;
        })
        .join(' ');
};

const input = '1.k8-i8 g7-j7; 2.k5-j5 h6-h9; 3.k7-k9 f8-c8;';
console.log(input);
console.log(transformGame(input));

Output:

1.k8-i8 g7-j7; 2.k5-j5 h6-h9; 3.k7-k9 f8-c8;
1.1h-3h 5g-2g; 2.1e-2e 4f-4i; 3.1g-1i 6h-9h;

Normalizing a board game notation

1 Answers1

Sample implementation