day 1, 2 java

README.md

@@ -8,4 +8,8 @@ inputs directory contains **my** inputs. Yours will be different
 
 ```shell
 go run 01.go < inputs/01.txt
+```
+
+```shell
+java day01.java < inputs/01.txt
 ```

day01.java

@@ -0,0 +1,26 @@
+import java.util.*;
+
+import static java.lang.Integer.parseInt;
+import static java.lang.Math.abs;
+import static java.lang.System.in;
+import static java.lang.System.out;
+
+public class day01 {
+    public static void main(String[] args) {
+        var left = new ArrayList<Integer>();
+        var right = new ArrayList<Integer>();
+        new Scanner(in).findAll("(\\d+)\\s+(\\d+)").forEach(pair -> {
+            left.add(parseInt(pair.group(1)));
+            right.add(parseInt(pair.group(2)));
+        });
+        left.sort(Integer::compareTo);
+        right.sort(Integer::compareTo);
+        int total = 0, similarity = 0;
+        for (int i = 0; i < left.size(); i++) {
+            int l = left.get(i);
+            total += abs(l - right.get(i));
+            similarity += (int) (l * right.stream().filter(n -> n.equals(l)).count());
+        }
+        out.println(total + " " + similarity);
+    }
+}

day02.java

@@ -0,0 +1,49 @@
+import java.io.*;
+import java.util.*;
+
+import static java.lang.System.in;
+import static java.lang.System.out;
+
+public class day02 {
+    public static void main(String[] args) {
+        var safes = new int[]{0, 0};
+        new BufferedReader(new InputStreamReader(in)).lines().forEach(line -> {
+            var report = new Report(line);
+            if (report.safe()) {
+                safes[0]++;
+                safes[1]++;
+            } else if (report.canBeSafe()) {
+                safes[1]++;
+            }
+        });
+        out.println(safes[0] + " " + safes[1]);
+    }
+
+    static class Report extends ArrayList<Integer> {
+        Report(String input) {
+            super(Arrays.stream(input.split("\\s")).map(Integer::valueOf).toList());
+        }
+
+        Report(List<Integer> source, int except) {
+            super(source);
+            remove(except);
+        }
+
+        boolean safe() {
+            boolean increasing = getFirst().compareTo(getLast()) < 0;
+            for (int i = 1; i < size(); i++) {
+                if (increasing && (get(i) - get(i - 1) <= 0 || get(i) - get(i - 1) > 3) ||
+                    !increasing && (get(i) - get(i - 1) >= 0 || get(i - 1) - get(i) > 3)) {
+                    return false;
+                }
+            }
+            return true;
+        }
+
+       boolean canBeSafe() {
+            for (int i = 0; i < size(); i++)
+                if (new Report(this, i).safe()) return true;
+            return false;
+        }
+    }
+}