Summary
- The data is in a grid.
Os can roll, #s can not, .s are empty space.- “tilt” north so all roll-able rocks roll north.
- All the “load” value on the north wall. The values of rocks on row 0 are
rock_count * (len(grid) - index)
Full challenge: Day 14
Stealing from my playbook of Day 13’s Vertical Reflection Points
I’m going to rotate the entire grid clockwise. The pros for this to me are:
- “Normal” Loop when calculating the roll, left to right.
- Value calc will be
rock_count * index
In all challenges so far, my default way of importing the data is to read the
file and split by \n. This gives me an array, string[], which each element
being a row. From that this is how I then rotated it:
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function rotate_raw(data: string[]){
let rotated_data: string[][] = [];
let count: number = -1;
data.forEach((row) => {
row.split('').forEach((cell, index) => {
if (count < index){
rotated_data.push([cell]);
count++;
}else{
rotated_data[index].push(cell);
}
});
});
rotated_data.forEach((row) => {
row.reverse();
});
return rotated_data;
};
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Rolling
Now that the data is in a format I like I need to figure out how to “roll” the
rocks. Luckily, data[0][0] (which was the bottom left corner) is now the top
left! I can scan left-to-right, picking up Os as I encounter them and once I
hit a barrier I can “back up” placing rocks as I go.
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function tilt_data(data: string[][]): string[][]{
for (let i = 0; i < data.length; i++){
let rollable_count: number = 0
for (let j = 0; j < data[i].length; j++){
if (data[i][j] === 'O'){
// Pick up rocks
rollable_count++;
data[i][j] = '.';
}else if (data[i][j] === '#' && rollable_count !== 0){
// Back up, drop rocks.
// Note: we should always have enough room
for (let k = 0; k < rollable_count; k++){
data[i][j-(1+k)] = 'O';
};
rollable_count = 0;
}
};
if (rollable_count !== 0){
// hit the end while still holding rocks
const last_index = data[i].length - 1;
for (let k = 0; k < rollable_count; k++){
data[i][last_index-k] = 'O';
};
}
};
return data;
}
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Getting the Sum
Because the data was rotated it’s as easy as looping an adding the index of item
in the row to the total.
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let sum: number = 0;
for (let i = 0; i < tilted_data.length; i++){
for (let j = 0; j < tilted_data[i].length; j++){
if (tilted_data[i][j] == 'O'){
sum += j+1;
}
};
};
console.log(`Sum => ${sum}`);
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On to Part 2!