src/main/java/MainExercises.java

@@ -1,3 +1,5 @@
+import java.util.ArrayList;
+
 public class MainExercises
 {
     /*
@@ -21,7 +23,26 @@ public class MainExercises
     public char[][] generateTriangle(int n) {
 
         // todo
-        return null;
+        char[][] triangle = new char[n][];
+        for (int i = 0; i < n; i++) {
+            if (i == 0) {
+                triangle[0][0] = '*';
+            }
+            else if (i < (n - 1) && i > 0) {
+                for (int j = 0; j <= i; j++) {
+                    if (j == 0 || j == i) {
+                        triangle[i][j] = '*';
+                    }
+                    else triangle[i][j] = ' ';
+                }
+            }
+            else if (i == (n - 1)) {
+                for (int k = 0; k < n; k++) {
+                    triangle[i][k] = '*';
+                }
+            }
+        }
+        return triangle;
 
     }
 
@@ -59,7 +80,49 @@ public class MainExercises
    */
     public int[] spiralTraversal(int[][] matrix) {
         // todo
-        return null;
+        if (matrix == null || matrix.length == 0) {
+            return new int[0];
+        }
+
+        int rows = matrix.length;
+        int cols = matrix[0].length;
+
+        int[] result = new int[rows * cols];
+        int index = 0;
+
+        int top = 0;
+        int bottom = rows - 1;
+        int left = 0;
+        int right = cols - 1;
+
+        while (top <= bottom && left <= right) {
+
+            for (int i = left; i <= right; i++) {
+                result[index++] = matrix[top][i];
+            }
+            top++;
+
+            for (int i = top; i <= bottom; i++) {
+                result[index++] = matrix[i][right];
+            }
+            right--;
+
+            if (top <= bottom) {
+                for (int i = right; i >= left; i--) {
+                    result[index++] = matrix[bottom][i];
+                }
+                bottom--;
+            }
+
+            if (left <= right) {
+                for (int i = bottom; i >= top; i--) {
+                    result[index++] = matrix[i][left];
+                }
+                left++;
+            }
+        }
+
+        return result;
     }
 
     /*
@@ -90,13 +153,29 @@ public class MainExercises
         body to use them instead of arrays.
     */
 
-    public int[][] intPartitions(int n) {
-        // todo
-        return null;
+    public static ArrayList<ArrayList<Integer>> intPartitions(int n) {
+        ArrayList<ArrayList<Integer>> result = new ArrayList<>();
+        backtrack(n, n, new ArrayList<>(), result);
+        return result;
     }
 
+    private static void backtrack(int remaining, int max,
+                                  ArrayList<Integer> current,
+                                  ArrayList<ArrayList<Integer>> result) {
 
-    public static void main()
+        if (remaining == 0) {
+            result.add(new ArrayList<>(current));
+            return;
+        }
+
+        for (int i = Math.min(max, remaining); i >= 1; i--) {
+            current.add(i);
+            backtrack(remaining - i, i, current, result);
+            current.remove(current.size() - 1); // backtrack
+        }
+    }
+
+    static void main()
     {
 
     }