Complete main and bonus exercises

src/main/java/BonusExercises.java

@@ -20,7 +20,10 @@ public class BonusExercises {
             - Each segment (between dots) must follow same hyphen rules
      */
     public boolean validateEmail(String email) {
-        String regex = ""; // todo
+        String local = "[a-zA-Z0-9_]+(\\.[a-zA-Z0-9_]+)*";
+        String domainSegment = "[a-zA-Z0-9]([a-zA-Z0-9\\-]*[a-zA-Z0-9])?";
+        String domain = domainSegment + "(\\." + domainSegment + ")*";
+        String regex = "^" + local + "@" + domain + "$";
         Pattern pattern = Pattern.compile(regex);
         Matcher matcher = pattern.matcher(email);
 
@@ -39,7 +42,20 @@ public class BonusExercises {
         If no match for a date is found in the string, return null.
     */
     public String findDate(String string) {
-        // todo
+        String dayOrMonth = "(0[1-9]|[12][0-9]|3[01])";
+        String month = "(0[1-9]|1[0-2])";
+        String year = "[0-9]{4}";
+
+        String[] patterns = {
+                dayOrMonth + "/" + month + "/" + year,
+                year + "-" + month + "-" + dayOrMonth,
+                year + "/" + month + "/" + dayOrMonth
+        };
+
+        for (String pat : patterns) {
+            Matcher m = Pattern.compile(pat).matcher(string);
+            if (m.find()) return m.group();
+        }
         return null;
     }
 
@@ -54,8 +70,11 @@ public class BonusExercises {
         - has no white-space in it
      */
     public int findValidPasswords(String string) {
-        // todo
+        String regex = "(?=\\S{8,})(?=\\S*[A-Z])(?=\\S*[a-z])(?=\\S*\\d)(?=\\S*[!@#$%^&*])\\S+";
-        return -1;
+        Matcher m = Pattern.compile(regex).matcher(string);
+        int count = 0;
+        while (m.find()) count++;
+        return count;
     }
 
     /*
@@ -66,10 +85,25 @@ public class BonusExercises {
      */
     public List<String> findPalindromes(String string) {
         List<String> list = new ArrayList<>();
-        // todo
+        Matcher m = Pattern.compile("[a-zA-Z]+").matcher(string);
+        while (m.find()) {
+            String word = m.group();
+            if (word.length() >= 3 && isPalindrome(word)) {
+                list.add(word);
+            }
+        }
         return list;
     }
 
+    private boolean isPalindrome(String s) {
+        String lower = s.toLowerCase();
+        int left = 0, right = lower.length() - 1;
+        while (left < right) {
+            if (lower.charAt(left++) != lower.charAt(right--)) return false;
+        }
+        return true;
+    }
+
     public static void main(String[] args) {
         // you can test your code here
     }

src/main/java/MainExercises.java

@@ -1,3 +1,7 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
 public class MainExercises
 {
     /*
@@ -19,10 +23,20 @@ public class MainExercises
     the output has to be a two-dimensional array of characters, so don't just print the triangle!
  */
     public char[][] generateTriangle(int n) {
+        if (n == 0) return new char[0][];
 
-        // todo
+        char[][] triangle = new char[n][];
-        return null;
+        for (int i = 0; i < n; i++) {
-
+            triangle[i] = new char[i + 1];
+            if (i <= 1 || i == n - 1) {
+                Arrays.fill(triangle[i], '*');
+            } else {
+                triangle[i][0] = '*';
+                Arrays.fill(triangle[i], 1, i, ' ');
+                triangle[i][i] = '*';
+            }
+        }
+        return triangle;
     }
 
 
@@ -58,8 +72,33 @@ public class MainExercises
            - Number of columns: matrix[0].length (if rectangular)
    */
     public int[] spiralTraversal(int[][] matrix) {
-        // todo
+        if (matrix == null || matrix.length == 0) return new int[0];
-        return null;
+
+        int rows = matrix.length;
+        int cols = matrix[0].length;
+        int[] result = new int[rows * cols];
+        int idx = 0;
+
+        int top = 0, bottom = rows - 1, left = 0, right = cols - 1;
+
+        while (top <= bottom && left <= right) {
+            for (int j = left; j <= right; j++) result[idx++] = matrix[top][j];
+            top++;
+
+            for (int i = top; i <= bottom; i++) result[idx++] = matrix[i][right];
+            right--;
+
+            if (top <= bottom) {
+                for (int j = right; j >= left; j--) result[idx++] = matrix[bottom][j];
+                bottom--;
+            }
+
+            if (left <= right) {
+                for (int i = bottom; i >= top; i--) result[idx++] = matrix[i][left];
+                left++;
+            }
+        }
+        return result;
     }
 
     /*
@@ -91,8 +130,20 @@ public class MainExercises
     */
 
     public int[][] intPartitions(int n) {
-        // todo
+        List<int[]> result = new ArrayList<>();
-        return null;
+        generatePartitions(n, n, new int[n], 0, result);
+        return result.toArray(new int[0][]);
+    }
+
+    private void generatePartitions(int remaining, int maxPart, int[] current, int depth, List<int[]> result) {
+        if (remaining == 0) {
+            result.add(Arrays.copyOf(current, depth));
+            return;
+        }
+        for (int part = Math.min(remaining, maxPart); part >= 1; part--) {
+            current[depth] = part;
+            generatePartitions(remaining - part, part, current, depth + 1, result);
+        }
     }
 
 
@@ -100,4 +151,4 @@ public class MainExercises
     {
 
     }
-}
+}