Add solution for Day 1 in Java

Advent of Code/2023/Day1.java

@@ -0,0 +1,107 @@
+import java.util.List;
+import java.util.Scanner;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.util.ArrayList;
+import java.io.File;
+
+public class Day1 {
+    public static void main(String[] args) {
+        try {
+            part1();
+            part2();
+        } catch (Exception e) {
+            System.err.println("Error: " + e.getMessage());
+        }
+    }
+
+    /*
+     * Process each line as characters, filter out those corresponding to digits
+     *, and get the number formed by the first and last digits within the line. 
+     * If there is only 1 digit in the line, then use that digit twice.
+     * That is the calibration value.
+     */
+    private static Integer processLinePart1(String line) {
+        List<Character> tokens = new ArrayList<Character>();
+        for (int i = 0; i < line.length(); i++) {
+            char ch = line.charAt(i);
+            if (ch >= '0' && ch <= '9') {
+                tokens.add(ch);
+            }
+        }
+        if (line.length() > 1) {
+            return Integer.parseInt("" + tokens.get(0) + tokens.get(tokens.size() - 1));
+        } else {
+            return Integer.parseInt("" + tokens.get(0) + tokens.get(0));
+        }
+    }
+
+    /*
+     * Process each line using regular expressions and modify words to respective digits.
+     * Get the number formed by the first and last digits within the line as in part 1. 
+     * If there is only 1 digit in the line, then use that digit twice.
+     * That is the calibration value.
+     */
+    private static Integer processLinePart2(String line) {
+        Pattern pattern = Pattern.compile("(one|two|three|four|five|six|seven|eight|nine|\\d)");
+        Matcher m = pattern.matcher(line);
+        List<String> groups = new ArrayList<String>();
+        while(m.find()) {
+            String group = m.group(1);
+            if (Pattern.compile("\\d").matcher(group).matches()) {
+                groups.add(group);
+            } else {
+                switch(group) {
+                    case "one": groups.add("1");
+                                break;
+                    case "two": groups.add("2");
+                                break;
+                    case "three": groups.add("3");
+                                break;
+                    case "four": groups.add("4");
+                                break;
+                    case "five": groups.add("5");
+                                break;
+                    case "six": groups.add("6");
+                                break;
+                    case "seven": groups.add("7");
+                                break;
+                    case "eight": groups.add("8");
+                                break;
+                    case "nine": groups.add("9");
+                                break;                    
+                }
+            }
+        }
+        if (line.length() > 1) {
+            return Integer.parseInt("" + groups.get(0) + groups.get(groups.size() - 1));
+        } else {
+            return Integer.parseInt("" + groups.get(0) + groups.get(0));
+        }
+    }
+
+    public static void part1() throws Exception {
+        Scanner sc = new Scanner(new File("test.in"));
+        int sum = 0;
+        while(sc.hasNextLine()) {
+            String line = sc.nextLine();
+            int calibrationValue = processLinePart1(line);
+            sum += calibrationValue;
+        }
+        sc.close();
+        System.out.println(sum);
+    }
+
+     public static void part2() throws Exception {
+         Scanner sc = new Scanner(new File("test.in"));
+         int sum = 0;
+
+        while(sc.hasNextLine()) {
+             String line = sc.nextLine();
+             int calibrationValue = processLinePart2(line);
+             sum += calibrationValue;
+         }
+         sc.close();
+         System.out.println(sum);
+     }
+}