66. Binary Tree Preorder Traversal

66. Binary Tree Preorder Traversal

Description

Given a binary tree, return the preorder traversal of its nodes' values.

Example

Given:
    1
   / \
  2   3
 / \
4   5
return [1,2,4,5,3].

Solution

import java.util.*;
/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */

public class Solution {
    /**
     * @param root: A Tree
     * @return: Preorder in ArrayList which contains node values.
     */
    List<Integer> list = new ArrayList<Integer>();
    public List<Integer> preorderTraversal(TreeNode root) {
        // write your code here
        if(root!=null){
            list.add(root.val);
            preorderTraversal(root.left);
            preorderTraversal(root.right);
        }
        return list;
    }
}