Data commit

Task/Negative-base-numbers/Java/negative-base-numbers.java

@@ -0,0 +1,53 @@
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+
+public class NegativeBaseNumbers {
+    private static final String DIGITS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
+
+    private static String encodeNegBase(long n, int b) {
+        if (b < -62 || b > -1) throw new IllegalArgumentException("Parameter b is out of bounds");
+        if (n == 0) return "0";
+        StringBuilder out = new StringBuilder();
+        long nn = n;
+        while (nn != 0) {
+            int rem = (int) (nn % b);
+            nn /= b;
+            if (rem < 0) {
+                nn++;
+                rem -= b;
+            }
+            out.append(DIGITS.charAt(rem));
+        }
+        out.reverse();
+        return out.toString();
+    }
+
+    private static long decodeNegBase(String ns, int b) {
+        if (b < -62 || b > -1) throw new IllegalArgumentException("Parameter b is out of bounds");
+        if (Objects.equals(ns, "0")) return 0;
+        long total = 0;
+        long bb = 1;
+        for (int i = ns.length() - 1; i >= 0; i--) {
+            char c = ns.charAt(i);
+            total += DIGITS.indexOf(c) * bb;
+            bb *= b;
+        }
+        return total;
+    }
+
+    public static void main(String[] args) {
+        List<Map.Entry<Long, Integer>> nbl = List.of(
+                Map.entry(10L, -2),
+                Map.entry(146L, -3),
+                Map.entry(15L, -10),
+                Map.entry(-4393346L, -62)
+        );
+        for (Map.Entry<Long, Integer> p : nbl) {
+            String ns = encodeNegBase(p.getKey(), p.getValue());
+            System.out.printf("%12d encoded in base %-3d = %s\n", p.getKey(), p.getValue(), ns);
+            long n = decodeNegBase(ns, p.getValue());
+            System.out.printf("%12s decoded in base %-3d = %d\n\n", ns, p.getValue(), n);
+        }
+    }
+}