Add: SRM 633 Div2 Medium

Author: junk0612

Diff for: TopCoder/SRMs/SRM633/Div2_500_ABBA/ABBA.java

@@ -0,0 +1,35 @@
+import java.util.HashMap;
+
+public class ABBA {
+	private HashMap<String, Boolean> map = new HashMap<String, Boolean>();
+
+	public String canObtain(String initial, String target) {
+		if (isPossible(initial, target))
+			return "Possible";
+		return "Impossible";
+	}
+
+	private boolean isPossible(String initial, String target) {
+		if (map.containsKey(target)) {
+			return map.get(target);
+		}
+		if (initial.equals(target)) {
+			map.put(target, true);
+		} else if (initial.length() >= target.length()) {
+			map.put(target, false);
+		} else {
+			boolean b = false;
+			if (target.endsWith("A")) {
+				b |= isPossible(initial,
+						target.substring(0, target.length() - 1));
+			} else {
+				b |= isPossible(
+						initial,
+						new StringBuilder(target.substring(0,
+								target.length() - 1)).reverse().toString());
+			}
+			map.put(target, b);
+		}
+		return map.get(target);
+	}
+}