Initial data commit

Task/Ordered-partitions/Java/ordered-partitions.java

@@ -0,0 +1,72 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+public final class OrderedPartitions {
+
+	public static void main(String[] aArgs) {
+		List<Integer> sizes = ( aArgs == null || aArgs.length == 0 ) ?
+			List.of( 2, 0, 2 ) : Arrays.stream(aArgs).map( s -> Integer.valueOf(s) ).toList();
+		
+		System.out.println("Partitions for " + sizes + ":");
+		final int total = sizes.stream().reduce(0, Integer::sum);
+		List<Integer> permutation = IntStream.rangeClosed(1, total).boxed().collect(Collectors.toList());
+	
+		while ( hasNextPermutation(permutation) ) {
+	        List<List<Integer>> partition = new ArrayList<List<Integer>>();
+	        int sum = 0;
+	        boolean isValid = true;
+	        for ( int size : sizes ) {
+            	List<Integer> subList = permutation.subList(sum, sum + size);
+                if ( ! isIncreasing(subList) ) {
+                    isValid = false;
+                    break;
+                }
+                partition.add(subList);
+	            sum += size;
+	        }
+	
+	        if ( isValid ) {
+	        	System.out.println(" ".repeat(4) + partition);
+	        }	
+	    }
+	}
+	
+	private static boolean hasNextPermutation(List<Integer> aPerm) {
+	    final int lastIndex = aPerm.size() - 1;
+	    int i = lastIndex;
+	    while ( i > 0 && aPerm.get(i - 1) >= aPerm.get(i) ) {
+	        i--;
+	    }
+	
+	    if ( i <= 0 ) {
+	        return false;
+	    }
+	
+	    int j = lastIndex;
+	    while ( aPerm.get(j) <= aPerm.get(i - 1) ) {
+	        j--;
+	    }	
+	    swap(aPerm, i - 1, j);
+	
+	    j = lastIndex;
+	    while ( i < j ) {
+	    	swap(aPerm, i++, j--);
+	    }
+	
+	    return true;
+	}
+	
+	private static boolean isIncreasing(List<Integer> aList) {
+	    return aList.stream().sorted().toList().equals(aList);
+	}
+	
+	private static void swap(List<Integer> aList, int aOne, int aTwo) {
+		final int temp = aList.get(aOne);
+	    aList.set(aOne, aList.get(aTwo));
+	    aList.set(aTwo, temp);
+	}
+
+}