Lintcode/src/chapter3_binary_tree_and_divide_and_conquer/BinaryTreePreorderTraversal.java

fishercoder1534 · fishercoder1534 · commit c5012136a10c · 2016-09-08T21:23:39.000-07:00
diff --git a/Lintcode/src/chapter3_binary_tree_and_divide_and_conquer/BinaryTreePreorderTraversal.java b/Lintcode/src/chapter3_binary_tree_and_divide_and_conquer/BinaryTreePreorderTraversal.java
@@ -0,0 +1,30 @@
+package chapter3_binary_tree_and_divide_and_conquer;
+
+import java.util.ArrayList;
+
+import classes.TreeNode;
+
+public class BinaryTreePreorderTraversal {
+
+    /**
+     * @param root: The root of binary tree.
+     * @return: Preorder in ArrayList which contains node values.
+     */
+    
+    //easily 1 min AC! Cheers!
+    public ArrayList<Integer> preorderTraversal(TreeNode root) {
+        // write your code here
+        ArrayList<Integer> list = new ArrayList<Integer>();
+        dfs(root, list);
+        return list;
+    }
+    
+    void dfs(TreeNode root, ArrayList<Integer> list){
+        if(root == null) return;
+        list.add(root.val);
+        dfs(root.left, list);
+        dfs(root.right, list);
+        return;
+    }
+
+}
