Day 4 assignment
“Looks like the Chief’s not here. Next!” One of The Historians pulls out a device and pushes the only button on it. After a brief flash, you recognize the interior of the Ceres monitoring station!
Solution in Java
Full source can be found: in GitHub
Part 1
For the first part of today I chose to re-use my CharGrid class. With this I can iterate of all of the columns and rows looking for the X in any spot.
For each of the matches I find the code looks at all the neighbours to find the letter M, and if that is found continues for the remainder A and S in the same direction.
1public void part1() {
2 var counted = 0;
3 var grid = inputLoader.charGrid();
4
5 for (var start : grid.findChar('X')) {
6 var neighbours = start.allNeighbours();
7 for (var neighbour : neighbours) {
8 if (grid.at(neighbour) == 'M') {
9 var direction = new Vector(start, neighbour).direction();
10 var aCheck = neighbour.translate(direction);
11 var sCheck = aCheck.translate(direction);
12
13 if (grid.at(aCheck) == 'A' && grid.at(sCheck) == 'S') {
14 counted++;
15 }
16 }
17 }
18 }
19
20 validator.part1(counted);
21}
Part 2
For part 2 the logic is changed to look for the MAS text in an X shape. Which simplifies to looking as I only have to locate all A characters and then start looking to the corners to find the letters M and opposite of it the S.
1public void part2() {
2 var counted = 0;
3 var grid = inputLoader.charGrid();
4
5 for (var start : grid.findChar('A')) {
6 var tlbrValid = grid.at(start.left().up()) == 'M' && grid.at(start.right().down()) == 'S';
7 var brtlValid = grid.at(start.down().right()) == 'M' && grid.at(start.up().left()) == 'S';
8
9 var bltrValid = grid.at(start.left().down()) == 'M' && grid.at(start.right().up()) == 'S';
10 var trblValid = grid.at(start.up().right()) == 'M' && grid.at(start.down().left()) == 'S';
11
12 if ((tlbrValid || brtlValid) && (bltrValid || trblValid)) {
13 counted++;
14 }
15 }
16
17 validator.part2(counted);
18}