refactor 145

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/_145.java

@@ -7,7 +7,10 @@
 import java.util.List;
 import java.util.Stack;
 
-/**Given a binary tree, return the postorder traversal of its nodes' values.
+/**
+ * 145. Binary Tree Postorder Traversal
+
+ Given a binary tree, return the postorder traversal of its nodes' values.
 
  For example:
  Given binary tree {1,#,2,3},
@@ -21,40 +24,48 @@
  Note: Recursive solution is trivial, could you do it iteratively?*/
 
 public class _145 {
-	/**A tricky one: Modify the code for pre-order traversal so that it becomes root->right->left, and then reverse the result to get left->right->root.*/
-    public static List<Integer> postorderTraversal_iterative(TreeNode root) {
-        List<Integer> result = new ArrayList();
-        if (root == null) {
-            return result;
+  public static class Solution1 {
+    /**
+     * A tricky one: Modify the code for pre-order traversal
+     * so that it becomes root->right->left,
+     * and then reverse the result to get left->right->root.
+     */
+    public static List<Integer> postorderTraversal(TreeNode root) {
+      List<Integer> result = new ArrayList();
+      if (root == null) {
+        return result;
+      }
+      Stack<TreeNode> stack = new Stack();
+      stack.push(root);
+      while (!stack.isEmpty()) {
+        root = stack.pop();
+        result.add(root.val);
+        if (root.left != null) {
+          stack.push(root.left);
         }
-        Stack<TreeNode> stack = new Stack();
-        stack.push(root);
-        while (!stack.isEmpty()) {
-            root = stack.pop();
-            result.add(root.val);
-            if (root.left != null) {
-                stack.push(root.left);
-            }
-            if (root.right != null) {
-                stack.push(root.right);
-            }
+        if (root.right != null) {
+          stack.push(root.right);
         }
-        Collections.reverse(result);
-        return result;
+      }
+      Collections.reverse(result);
+      return result;
     }
+  }
 
-    public List<Integer> postorderTraversal_recursive(TreeNode root) {
-        List<Integer> result = new ArrayList();
-        return post(root, result);
+  public static class Solution2 {
+    public List<Integer> postorderTraversal(TreeNode root) {
+      List<Integer> result = new ArrayList();
+      return post(root, result);
     }
 
     List<Integer> post(TreeNode root, List<Integer> result) {
-        if (root == null) {
-            return result;
-        }
-        post(root.left, result);
-        post(root.right, result);
-        result.add(root.val);
+      if (root == null) {
         return result;
+      }
+      post(root.left, result);
+      post(root.right, result);
+      result.add(root.val);
+      return result;
     }
+  }
 }