Merge pull request #922 from beingshub02/main

Create preorder_traversal.java

Author: Sirajmolla

preorder_traversal.java

@@ -0,0 +1,36 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+    public List<Integer> preorderTraversal(TreeNode root) {
+        List<Integer> li = new ArrayList<>();
+        preorder(root,li);
+        return li;
+    }
+    
+     public List<Integer> preorder(TreeNode root,List<Integer> li){
+        if(root==null){
+            return li;
+        }
+    
+        li.add(root.val);
+        preorder(root.left,li);
+       preorder(root.right,li);
+        
+ 
+        return li;
+    }
+    
+}