Update PseudoPalindromicPath.java

src/PseudoPalindromicPath.java

@@ -8,45 +8,33 @@
  * @author LBW
  */
 public class PseudoPalindromicPath {
-    private int result = 0;
-    public int pseudoPalindromicPaths (TreeNode root) {
-        ArrayList<Integer> path = new ArrayList<>();
-        result = 0;
-        dfs(root, path);
-
-        return result;
-    }
-    private void dfs(TreeNode root, ArrayList<Integer> path) {
-        path.add(root.val);
-        if (root.left == null && root.right == null) {  //到叶节点了，path已经构建完毕，可以判断是否为回文序列了。
-            if (isPseudoPalindrome(path))
-                result += 1;
+
+    static class MyList extends ArrayList<Integer> {
+        @Override
+        public boolean add(Integer integer) {
+            if (contains(integer)) {
+                remove(integer);
+                return true;
+            }
+            return super.add(integer);
         }
-        if (root.left != null)
-            dfs(root.left, new ArrayList<>(path));
-        if (root.right != null)
-            dfs(root.right, new ArrayList<>(path));
+    }
+
+    public int pseudoPalindromicPaths(TreeNode root) {
+        return getCount(new MyList(), root);
     }
 
-    private boolean isPseudoPalindrome(ArrayList<Integer> path) {
-        Hashtable<Integer, Integer> hashtable = new Hashtable<>();
-
-        for (Integer i: path) {
-            if (!hashtable.containsKey(i)) {
-                hashtable.put(i, 1);
-            }
-            else {
-                hashtable.put(i, hashtable.get(i)+1);
-            }
-        }
-        int oddCount = 0;
-        for (Map.Entry<Integer, Integer> entry: hashtable.entrySet()) {
-            if (entry.getValue() % 2 == 1)
-                oddCount += 1;
-            if (oddCount > 1)
-                return false;
+    private int getCount(MyList list, TreeNode root) {
+        if (root == null) return 0;
+
+        list.add(root.val);
+
+        if (root.left == null && root.right == null) {
+            return list.size() > 1 ? 0 : 1;
+        } else {
+            return getCount((MyList) list.clone(), root.left) + 
+                   getCount((MyList) list.clone(), root.right);
         }
-        return true;
     }
 
     public static void main(String[] args) {