refactor 173

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/_173.java

@@ -8,91 +8,79 @@
 
 /**
  * 173. Binary Search Tree Iterator
+ *
  * Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.
- * <p>
+ *
  * Calling next() will return the next smallest number in the BST.
- * <p>
+ *
  * Note: next() and hasNext() should run in average O(1) time and uses O(h) memory, where h is the height of the tree.
  */
 public class _173 {
 
-    public static class Solution1 {
+  public static class Solution1 {
 
-        public static class BSTIterator {
+    public static class BSTIterator {
+      private Queue<Integer> queue;
 
-            private Queue<Integer> queue;
-
-            /**
-             * My natural idea is to use a queue to hold all elements in the BST, traverse it while constructing the iterator, although
-             * this guarantees O(1) hasNext() and next() time, but it uses O(n) memory.
-             */
-            //Cheers! Made it AC'ed at first shot! Praise the Lord! Practice does make perfect!
-            //I created a new class to do it using Stack to meet O(h) memory: {@link fishercoder.algorithms._173_using_stack}
-            public BSTIterator(TreeNode root) {
-                queue = new LinkedList<>();
-                if (root != null) {
-                    dfs(root, queue);
-                }
-            }
-
-            private void dfs(TreeNode root, Queue<Integer> q) {
-                if (root.left != null) {
-                    dfs(root.left, q);
-                }
-                q.offer(root.val);
-                if (root.right != null) {
-                    dfs(root.right, q);
-                }
-            }
-
-            /**
-             * @return whether we have a next smallest number
-             */
-            public boolean hasNext() {
-                return !queue.isEmpty();
-            }
-
-            /**
-             * @return the next smallest number
-             */
-            public int next() {
-                return queue.poll();
-            }
+      public BSTIterator(TreeNode root) {
+        queue = new LinkedList<>();
+        if (root != null) {
+          dfs(root, queue);
         }
-    }
-
-    public static class Solution2 {
-        public static class BSTIterator {
-            /**
-             * This is a super cool/clever idea: use a stack to store all the current left nodes of the BST, when pop(), we
-             * push all its right nodes into the stack if there are any.
-             * This way, we use only O(h) memory for this iterator, this is a huge saving when the tree is huge
-             * since h could be much smaller than n. Cheers!
-             */
+      }
 
-            private Stack<TreeNode> stack;
+      private void dfs(TreeNode root, Queue<Integer> q) {
+        if (root.left != null) {
+          dfs(root.left, q);
+        }
+        q.offer(root.val);
+        if (root.right != null) {
+          dfs(root.right, q);
+        }
+      }
 
-            public BSTIterator(TreeNode root) {
-                stack = new Stack();
-                pushToStack(root, stack);
-            }
+      public boolean hasNext() {
+        return !queue.isEmpty();
+      }
 
-            private void pushToStack(TreeNode root, Stack<TreeNode> stack) {
-                while (root != null) {
-                    stack.push(root);
-                    root = root.left;
-                }
-            }
+      public int next() {
+        return queue.poll();
+      }
+    }
+  }
+
+  public static class Solution2 {
+    public static class BSTIterator {
+      /**
+       * This is a super cool/clever idea: use a stack to store all the current left nodes of the BST, when pop(), we
+       * push all its right nodes into the stack if there are any.
+       * This way, we use only O(h) memory for this iterator, this is a huge saving when the tree is huge
+       * since h could be much smaller than n. Cheers!
+       */
+
+      private Stack<TreeNode> stack;
+
+      public BSTIterator(TreeNode root) {
+        stack = new Stack();
+        pushToStack(root, stack);
+      }
+
+      private void pushToStack(TreeNode root, Stack<TreeNode> stack) {
+        while (root != null) {
+          stack.push(root);
+          root = root.left;
+        }
+      }
 
-            public boolean hasNext() {
-                return !stack.isEmpty();
-            }
+      public boolean hasNext() {
+        return !stack.isEmpty();
+      }
 
-            public int next() {
-                TreeNode curr = stack.pop();
-                pushToStack(curr.right, stack);
-                return curr.val;
-            }
-        }
+      public int next() {
+        TreeNode curr = stack.pop();
+        pushToStack(curr.right, stack);
+        return curr.val;
+      }
     }
+  }
 }