1 files changed, 189 insertions, 0 deletions
diff --git a/day13/day13.java b/day13/day13.java
new file mode 100644
index 0000000..04f1b5f
--- /dev/null
+++ b/day13/day13.java
@@ -0,0 +1,189 @@
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.util.ArrayList;
+
+public class day13 {
+  public static void main(String args[]) throws IOException {
+    RandomAccessFile input = new RandomAccessFile("input", "r");
+    System.out.println("Day 13 Part 1: " + part1(input));
+    input.seek(0);
+    System.out.println("Day 13 Part 2: " + part2(input));
+    input.close();
+  }
+
+  public static String part1(RandomAccessFile input) throws IOException {
+    ArrayList<Pattern> patterns = new ArrayList<>();
+    Pattern pattern;
+    while ((pattern = getPattern(input)) != null) {
+      patterns.add(pattern);
+    }
+
+    int sum = 0;
+    for (Pattern p: patterns) {
+      sum += p.mirrorLine();
+    }
+    return Integer.toString(sum);
+  }
+
+  public static String part2(RandomAccessFile input) throws IOException {
+    ArrayList<Pattern> patterns = new ArrayList<>();
+    Pattern pattern;
+    while ((pattern = getPattern(input)) != null) {
+      patterns.add(pattern);
+    }
+
+    int sum = 0;
+    for (Pattern p: patterns) {
+      int line = p.mirrorLine();
+findSmudge:
+      for (int r = 0; r < p.rows(); r++) {
+        for (int c = 0; c < p.cols(); c++) {
+          p.repair(r, c);
+          int newline = p.differentMirrorLine(line);
+          p.repair(r, c);
+          if (newline > 0) {
+            sum += newline;
+            break findSmudge;
+          }
+        }
+      }
+    }
+    return Integer.toString(sum);
+  }
+
+  private static Pattern getPattern(RandomAccessFile input) throws IOException {
+    Pattern pattern = new Pattern();
+
+    String line = input.readLine();
+    while (line != null && line.length() != 0) {
+      pattern.add(line);
+      line = input.readLine();
+    }
+
+    if (pattern.rows() > 0) {
+      return pattern;
+    } else {
+      return null;
+    }
+  }
+
+  private static enum Terrain {
+    Ash,
+    Rock
+  }
+
+  private static class Pattern {
+    ArrayList<ArrayList<Terrain>> pattern;
+
+    public Pattern() {
+      this.pattern = new ArrayList<>();
+    }
+
+    public void add(String line) {
+      ArrayList<Terrain> row = new ArrayList<>();
+      for (char ch: line.toCharArray()) {
+        if (ch == '#') {
+          row.add(Terrain.Rock);
+        } else if (ch == '.') {
+          row.add(Terrain.Ash);
+        }
+      }
+      this.pattern.add(row);
+    }
+
+    public int rows() {
+      return this.pattern.size();
+    }
+
+    public int cols() {
+      return this.pattern.get(0).size();
+    }
+
+    public int mirrorLine() {
+      for (int i = 1; i < this.cols(); i++) {
+        boolean isMirrorLine = true;
+        for (ArrayList<Terrain> row: this.pattern) {
+          int l = i - 1, r = i;
+          while (isMirrorLine && l >= 0 && r < this.cols()) {
+            if (row.get(l) != row.get(r)) {
+              isMirrorLine = false;
+            }
+            l -= 1;
+            r += 1;
+          }
+        }
+        if (isMirrorLine) {
+          return i;
+        }
+      }
+      for (int i = 1; i < this.rows(); i++) {
+        boolean isMirrorLine = true;
+        int a = i - 1, b = i;
+        while (isMirrorLine && a >= 0 && b < this.rows()) {
+          ArrayList<Terrain> ra = this.pattern.get(a);
+          ArrayList<Terrain> rb = this.pattern.get(b);
+          for (int j = 0; j < this.cols(); j++) {
+            if (ra.get(j) != rb.get(j)) {
+              isMirrorLine = false;
+              break;
+            }
+          }
+          a -= 1;
+          b += 1;
+        }
+        if (isMirrorLine) {
+          return 100 * i;
+        }
+      }
+      return 0;
+    }
+
+    public int differentMirrorLine(int oldLine) {
+      for (int i = 1; i < this.cols(); i++) {
+        boolean isMirrorLine = true;
+        for (ArrayList<Terrain> row: this.pattern) {
+          int l = i - 1, r = i;
+          while (isMirrorLine && l >= 0 && r < this.cols()) {
+            if (row.get(l) != row.get(r)) {
+              isMirrorLine = false;
+            }
+            l -= 1;
+            r += 1;
+          }
+        }
+        if (isMirrorLine && i != oldLine) {
+          return i;
+        }
+      }
+      for (int i = 1; i < this.rows(); i++) {
+        boolean isMirrorLine = true;
+        int a = i - 1, b = i;
+        while (isMirrorLine && a >= 0 && b < this.rows()) {
+          ArrayList<Terrain> ra = this.pattern.get(a);
+          ArrayList<Terrain> rb = this.pattern.get(b);
+          for (int j = 0; j < this.cols(); j++) {
+            if (ra.get(j) != rb.get(j)) {
+              isMirrorLine = false;
+              break;
+            }
+          }
+          a -= 1;
+          b += 1;
+        }
+        if (isMirrorLine && (100 * i) != oldLine) {
+          return 100 * i;
+        }
+      }
+      return 0;
+    }
+
+    public void repair(int row, int col) {
+      Terrain smudge = this.pattern.get(row).get(col);
+      if (smudge == Terrain.Rock) {
+        this.pattern.get(row).set(col, Terrain.Ash);
+      } else {
+        this.pattern.get(row).set(col, Terrain.Rock);
+      }
+    }
+  }
+}