src/main/java/MainExercises.java

@@ -1,3 +1,5 @@
+import java.util.ArrayList;
+
 public class MainExercises
 {
     /*
@@ -145,8 +147,62 @@ public class MainExercises
     */
 
     public int[][] intPartitions(int n) {
-        // todo
-        return null;
+
+        ArrayList<int[]> result = new ArrayList<>();
+        int[] current = new int[n]; // current partition, to be built
+
+        // we use stack arrays to have the situation saved.
+        int[] remainingStack = new int[n*n]; // remaining value, to be added
+//        int[] maxValueStack = new int[n*n]; // maximum number we can use, to prevent repeating partitions
+        int[] nextTryStack = new int[n*n]; // the next number we try
+        int[] lenStack = new int[n*n]; // length of current partition, gives us the next index in current
+        int head = 0; // works like a pointer, it makes stack arrays make sense.
+
+        remainingStack[0] = n;
+//        maxValueStack[0] = n;
+        nextTryStack[0] = n;
+        lenStack[0] = 0;
+
+        while(head >= 0){
+            int remaining = remainingStack[head];
+//            int maxValue = maxValueStack[head];
+            int nextTry = nextTryStack[head];
+            int partitionLen = lenStack[head];
+
+            if(remaining == 0){ // partition has been completed
+                //
+                int[] partition = new int[partitionLen];
+                System.arraycopy(current, 0, partition, 0, partitionLen);
+                result.add(partition);
+                head--;
+                continue;
+            }
+
+            if(nextTry <= 0){ // no choices left
+                head--;
+                continue;
+            }
+
+            int chosen = nextTry;
+            nextTryStack[head] = chosen - 1; // next value to be tried
+            current[partitionLen] = chosen; // adding selected number
+
+            // generating next number for the partition
+            head++;
+            remainingStack[head] = remaining - chosen;
+//            maxValueStack[head] = chosen;
+            nextTryStack[head] = Math.min(chosen, remaining - chosen);
+            lenStack[head] = partitionLen + 1;
+
+        }
+
+        int[][] output = new int[result.size()][];
+        for(int i = 0; i < result.size(); i++){
+            output[i] = result.get(i);
+        }
+
+        return output;
+
     }