tasks a-s

Task/Permutations/Java/permutations-1.java

@@ -0,0 +1,83 @@
+public class PermutationGenerator {
+    private int[] array;
+    private int firstNum;
+    private boolean firstReady = false;
+
+    public PermutationGenerator(int n, int firstNum_) {
+        if (n < 1) {
+            throw new IllegalArgumentException("The n must be min. 1");
+        }
+        firstNum = firstNum_;
+        array = new int[n];
+        reset();
+    }
+
+    public void reset() {
+        for (int i = 0; i < array.length; i++) {
+            array[i] = i + firstNum;
+        }
+        firstReady = false;
+    }
+
+    public boolean hasMore() {
+        boolean end = firstReady;
+        for (int i = 1; i < array.length; i++) {
+            end = end && array[i] < array[i-1];
+        }
+        return !end;
+    }
+
+    public int[] getNext() {
+
+        if (!firstReady) {
+            firstReady = true;
+            return array;
+        }
+
+        int temp;
+        int j = array.length - 2;
+        int k = array.length - 1;
+
+        // Find largest index j with a[j] < a[j+1]
+
+        for (;array[j] > array[j+1]; j--);
+
+        // Find index k such that a[k] is smallest integer
+        // greater than a[j] to the right of a[j]
+
+        for (;array[j] > array[k]; k--);
+
+        // Interchange a[j] and a[k]
+
+        temp = array[k];
+        array[k] = array[j];
+        array[j] = temp;
+
+        // Put tail end of permutation after jth position in increasing order
+
+        int r = array.length - 1;
+        int s = j + 1;
+
+        while (r > s) {
+            temp = array[s];
+            array[s++] = array[r];
+            array[r--] = temp;
+        }
+
+        return array;
+    } // getNext()
+
+    // For testing of the PermutationGenerator class
+    public static void main(String[] args) {
+        PermutationGenerator pg = new PermutationGenerator(3, 1);
+
+        while (pg.hasMore()) {
+            int[] temp =  pg.getNext();
+            for (int i = 0; i < temp.length; i++) {
+                System.out.print(temp[i] + " ");
+            }
+            System.out.println();
+        }
+    }
+
+} // class