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Puzzle3.java
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Puzzle3.java
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package advent2023;
import static java.nio.charset.StandardCharsets.UTF_8;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
/**
* @author Éamonn McManus
*/
public class Puzzle3 {
public static void main(String[] args) throws Exception {
try (InputStream in = Puzzle3.class.getResourceAsStream("puzzle3.txt")) {
String lineString = new String(in.readAllBytes(), UTF_8);
List<String> lines = List.of(lineString.split("\n"));
// Part 1
int sum = 0;
for (int i = 0; i < lines.size(); i++) {
String line = lines.get(i);
for (int j = 0; j < line.length(); ) {
if (Character.isDigit(line.charAt(j))) {
int end;
for (end = j + 1; end < line.length() && Character.isDigit(line.charAt(end)); end++) {}
if (sym(lines, i - 1, j - 1) || sym(lines, i, j - 1) || sym(lines, i + 1, j - 1)
|| sym(lines, i - 1, end) || sym(lines, i, end) || sym(lines, i + 1, end)
|| adjacent(lines, i, j, end)) {
sum += Integer.parseInt(line.substring(j, end));
}
j = end;
} else {
j++;
}
}
}
System.out.println("Sum is " + sum);
// Part 2
int ratioSum = 0;
// For each cell in the grid, record the number that starts in that cell, or 0 if none.
int[][] ints = new int[lines.size()][lines.get(0).length()];
for (int i = 0; i < lines.size(); i++) {
String line = lines.get(i);
for (int j = 0; j < line.length(); ) {
if (Character.isDigit(line.charAt(j))) {
int end;
for (end = j + 1; end < line.length() && Character.isDigit(line.charAt(end)); end++) {}
int n = Integer.parseInt(line.substring(j, end));
for (int jj = j; jj < end; jj++) {
ints[i][jj] = n;
}
j = end;
} else {
j++;
}
}
}
// Now scan for * symbols and find the adjacent numbers. This is a little tedious.
for (int i = 0; i < lines.size(); i++) {
String line = lines.get(i);
for (int j = 0; j < line.length(); j++) {
if (line.charAt(j) == '*') {
List<Integer> numbers = new ArrayList<>();
if (i > 0) {
if (ints[i - 1][j] > 0) {
numbers.add(ints[i - 1][j]);
} else {
if (j > 0 && ints[i - 1][j - 1] > 0) {
numbers.add(ints[i - 1][j - 1]);
}
if (j < line.length() && ints[i - 1][j + 1] > 0) {
numbers.add(ints[i - 1][j + 1]);
}
}
}
if (j > 0 && ints[i][j - 1] > 0) {
numbers.add(ints[i][j - 1]);
}
if (j < line.length() && ints[i][j + 1] > 0) {
numbers.add(ints[i][j + 1]);
}
if (i < lines.size() - 1) {
if (ints[i + 1][j] > 0) {
numbers.add(ints[i + 1][j]);
} else {
if (j > 0 && ints[i + 1][j - 1] > 0) {
numbers.add(ints[i + 1][j - 1]);
}
if (j < line.length() && ints[i + 1][j + 1] > 0) {
numbers.add(ints[i + 1][j + 1]);
}
}
}
assert numbers.size() < 3;
assert !numbers.contains(0);
if (numbers.size() == 2) {
ratioSum += numbers.get(0) * numbers.get(1);
}
}
}
}
System.out.println("Ratio sum " + ratioSum);
}
}
private static boolean sym(List<String> lines, int i, int j) {
if (i < 0 || i >= lines.size() || j < 0) {
return false;
}
String line = lines.get(i);
if (j >= line.length()) {
return false;
}
char c = line.charAt(j);
return c != '.' && !Character.isDigit(c);
}
private static boolean adjacent(List<String> lines, int i, int start, int end) {
for (int j = start; j < end; j++) {
if (sym(lines, i - 1, j) || sym(lines, i + 1, j)) {
return true;
}
}
return false;
}
}