home5

src/Node.java

@@ -8,15 +8,77 @@ public class Node {
    private Node nextSibling;
 
    Node (String n, Node d, Node r) {
-      // TODO!!! Your constructor here
+      this.name = n;
+      this.firstChild = d;
+      this.nextSibling = r;
    }
    
    public static Node parsePostfix (String s) {
-      return null;  // TODO!!! return the root
+      if (s.contains(",,")) {
+         throw new RuntimeException("double commas");
+      } else if (s.contains("\t")) {
+         throw new RuntimeException("tab char");
+      } else if (s.contains("()")) {
+         throw new RuntimeException("empty subtree");
+      } else if (s.contains(" ")) {
+         throw new RuntimeException("space");
+      } else if (s.contains("((") && s.contains("))")) {
+         throw new RuntimeException("Brackets");
+      } else if (s.contains(",") && !(s.contains("(") && s.contains(")"))) {
+         throw new RuntimeException("two roots");
+      }
+      String[] tokens = s.split("");
+      Stack<Node> stack = new Stack();
+      Node node = new Node(null, null, null);
+      boolean replacingRoot = false;
+      for (int i = 0; i < tokens.length; i++) {
+         String token = tokens[i].trim();
+         if (token.equals("(")) {
+            if (replacingRoot) {
+               throw new RuntimeException("Trying to replace root");
+            }
+            stack.push(node);
+            node.firstChild = new Node(null, null, null);
+            node = node.firstChild;
+            if (tokens[i+1].trim().equals(",")) {
+               throw new RuntimeException("comma after node");
+            }
+         } else if (token.equals(")")) {
+            node = stack.pop();
+            if (stack.size() == 0) {
+               replacingRoot = true;
+            }
+         } else if (token.equals(",")) {
+            if (replacingRoot) {
+               throw new RuntimeException("Trying to replace root");
+            }
+            node.nextSibling = new Node(null, null, null);
+            node = node.nextSibling;
+         } else {
+            if (node.name == null) {
+               node.name = token;
+            } else {
+               node.name += token;
+            }
+         }
+      }
+      return node;
    }
 
    public String leftParentheticRepresentation() {
-      return ""; // TODO!!! return the string without spaces
+      StringBuilder sb = new StringBuilder();
+      sb.append(this.name);
+      if (this.firstChild != null) {
+         sb.append("(");
+         sb.append(this.firstChild.leftParentheticRepresentation());
+         sb.append(")");
+      }
+
+      if (this.nextSibling != null) {
+         sb.append(",");
+         sb.append(this.nextSibling.leftParentheticRepresentation());
+      }
+      return sb.toString();
    }
 
    public static void main (String[] param) {