更新

exercise/src/Main.java

@@ -0,0 +1,59 @@
+import java.util.Scanner;
+
+public class Main {
+    static boolean isPrime(int x) {
+        if (x < 2)
+            return false;
+        if (x % 2 == 0)
+            return x == 2;
+        for (int i = 3; i * i <= x; i += 2) {
+            if (x % i == 0)
+                return false;
+        }
+        return true;
+    }
+
+    static boolean noZero(String s) {
+        for (int i = 0; i < s.length(); i++)
+            if (s.charAt(i) == '0')
+                return false;
+        return true;
+    }
+
+    public static void main(String[] args) {
+        Scanner in = new Scanner(System.in);
+        String s = in.next().trim();
+        boolean left = false, right = false;
+        if (noZero(s)) {
+            boolean ok = true;
+            for (int i = 0; i < s.length(); i++) {
+                int v = Integer.parseInt(s.substring(i));
+                if (!isPrime(v)) {
+                    ok = false;
+                    break;
+                }
+            }
+            left = ok;
+        }
+        if (noZero(s)) {
+            boolean ok = true;
+            for (int i = s.length(); i >= 1; i--) {
+                int v = Integer.parseInt(s.substring(0, i));
+                if (!isPrime(v)) {
+                    ok = false;
+                    break;
+                }
+            }
+            right = ok;
+        }
+        if (left && right)
+            System.out.println("both");
+        else if (left)
+            System.out.println("left");
+        else if (right)
+            System.out.println("right");
+        else
+            System.out.println("false");
+        in.close();
+    }
+}