Create 331. Verify Preorder Serialization of a Binary Tree.java

Author: futurus

331. Verify Preorder Serialization of a Binary Tree.java

@@ -0,0 +1,26 @@
+// NB:
+// - elements might contain more than 1 digit
+
+public class Solution {
+    public boolean isValidSerialization(String preorder) {
+        ArrayList<String> list = new ArrayList<String>();
+        String [] elems = preorder.split(",");
+
+        for (int i = 0; i < elems.length; i++) {
+            list.add(elems[i]);
+
+            while (list.size() > 2 
+            && list.get(list.size()-1).equals("#")
+            && list.get(list.size()-2).equals("#")
+            && !list.get(list.size()-3).equals("#")) {
+                // remove the two nulls
+                list.remove(list.size()-1); list.remove(list.size()-1); 
+                
+                // replace the last element with a null
+                list.remove(list.size()-1); list.add("#");
+            }
+        }
+
+        return (list.size() == 1 && list.get(0).equals("#"));
+    }
+}