Initial data commit

Task/Colorful-numbers/Java/colorful-numbers.java

@@ -0,0 +1,84 @@
+public class ColorfulNumbers {
+    private int count[] = new int[8];
+    private boolean used[] = new boolean[10];
+    private int largest = 0;
+
+    public static void main(String[] args) {
+        System.out.printf("Colorful numbers less than 100:\n");
+        for (int n = 0, count = 0; n < 100; ++n) {
+            if (isColorful(n))
+                System.out.printf("%2d%c", n, ++count % 10 == 0 ? '\n' : ' ');
+        }
+
+        ColorfulNumbers c = new ColorfulNumbers();
+
+        System.out.printf("\n\nLargest colorful number: %,d\n", c.largest);
+
+        System.out.printf("\nCount of colorful numbers by number of digits:\n");
+        int total = 0;
+        for (int d = 0; d < 8; ++d) {
+            System.out.printf("%d   %,d\n", d + 1, c.count[d]);
+            total += c.count[d];
+        }
+        System.out.printf("\nTotal: %,d\n", total);
+    }
+
+    private ColorfulNumbers() {
+        countColorful(0, 0, 0);
+    }
+
+    public static boolean isColorful(int n) {
+        // A colorful number cannot be greater than 98765432.
+        if (n < 0 || n > 98765432)
+            return false;
+        int digit_count[] = new int[10];
+        int digits[] = new int[8];
+        int num_digits = 0;
+        for (int m = n; m > 0; m /= 10) {
+            int d = m % 10;
+            if (n > 9 && (d == 0 || d == 1))
+                return false;
+            if (++digit_count[d] > 1)
+                return false;
+            digits[num_digits++] = d;
+        }
+        // Maximum number of products is (8 x 9) / 2.
+        int products[] = new int[36];
+        for (int i = 0, product_count = 0; i < num_digits; ++i) {
+            for (int j = i, p = 1; j < num_digits; ++j) {
+                p *= digits[j];
+                for (int k = 0; k < product_count; ++k) {
+                    if (products[k] == p)
+                        return false;
+                }
+                products[product_count++] = p;
+            }
+        }
+        return true;
+    }
+
+    private void countColorful(int taken, int n, int digits) {
+        if (taken == 0) {
+            for (int d = 0; d < 10; ++d) {
+                used[d] = true;
+                countColorful(d < 2 ? 9 : 1, d, 1);
+                used[d] = false;
+            }
+        } else {
+            if (isColorful(n)) {
+                ++count[digits - 1];
+                if (n > largest)
+                    largest = n;
+            }
+            if (taken < 9) {
+                for (int d = 2; d < 10; ++d) {
+                    if (!used[d]) {
+                        used[d] = true;
+                        countColorful(taken + 1, n * 10 + d, digits + 1);
+                        used[d] = false;
+                    }
+                }
+            }
+        }
+    }
+}