refactor 144

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/_144.java

@@ -8,71 +8,55 @@
 import java.util.List;
 import java.util.Stack;
 
-/**
- * 144. Binary Tree Preorder Traversal
-
- Given a binary tree, return the preorder traversal of its nodes' values.
-
- For example:
- Given binary tree {1,#,2,3},
- 1
-  \
-   2
-  /
- 3
- return [1,2,3].
-
- Note: Recursive solution is trivial, could you do it iteratively?*/
-
 public class _144 {
-  public static class Solution1 {
-    public List<Integer> preorderTraversal(TreeNode root) {
-      List<Integer> list = new ArrayList<>();
-      Stack<TreeNode> stack = new Stack<>();
-      stack.push(root);
-      while (!stack.isEmpty()) {
-        TreeNode curr = stack.pop();
-        if (curr != null) {
-          list.add(curr.val);
-          stack.push(curr.right);
-          stack.push(curr.left);
+    public static class Solution1 {
+        public List<Integer> preorderTraversal(TreeNode root) {
+            List<Integer> list = new ArrayList<>();
+            Stack<TreeNode> stack = new Stack<>();
+            stack.push(root);
+            while (!stack.isEmpty()) {
+                TreeNode curr = stack.pop();
+                if (curr != null) {
+                    list.add(curr.val);
+                    stack.push(curr.right);
+                    stack.push(curr.left);
+                }
+            }
+            return list;
         }
-      }
-      return list;
     }
-  }
 
-  public static class Solution2 {
-    public List<Integer> preorderTraversal(TreeNode root) {
-      List<Integer> list = new ArrayList();
-      return pre(root, list);
-    }
+    public static class Solution2 {
+        public List<Integer> preorderTraversal(TreeNode root) {
+            List<Integer> list = new ArrayList();
+            return pre(root, list);
+        }
 
-    List<Integer> pre(TreeNode root, List<Integer> list) {
-      if (root == null) {
-        return list;
-      }
-      list.add(root.val);
-      pre(root.left, list);
-      pre(root.right, list);
-      return list;
+        List<Integer> pre(TreeNode root, List<Integer> list) {
+            if (root == null) {
+                return list;
+            }
+            list.add(root.val);
+            pre(root.left, list);
+            pre(root.right, list);
+            return list;
+        }
     }
-  }
 
-  public static class Solution3 {
-    public List<Integer> preorderTraversal(TreeNode root) {
-      List<Integer> list = new ArrayList<>();
-      Stack<TreeNode> stack = new Stack<>();
-      while (!stack.isEmpty() || root != null) {
-        while (root != null) {
-          list.add(root.val);
-          stack.push(root);
-          root = root.left;
+    public static class Solution3 {
+        public List<Integer> preorderTraversal(TreeNode root) {
+            List<Integer> list = new ArrayList<>();
+            Stack<TreeNode> stack = new Stack<>();
+            while (!stack.isEmpty() || root != null) {
+                while (root != null) {
+                    list.add(root.val);
+                    stack.push(root);
+                    root = root.left;
+                }
+                root = stack.pop();
+                root = root.right;
+            }
+            return list;
         }
-        root = stack.pop();
-        root = root.right;
-      }
-      return list;
     }
-  }
 }