题解 | #二叉树的前序遍历#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return int整型一维数组
     */
    public List<Integer> list = new ArrayList();
    public int[] preorderTraversal (TreeNode root) {
        // write code here
        pT(root);
        int []ans = new int[list.size()];
        for(int i=0;i<ans.length;i++){
            ans[i]=list.get(i);
        }
        return ans;

        
    }
    public void pT(TreeNode node){
        if(node == null){
            return;
        }
        list.add(node.val);
        pT(node.left);
        pT(node.right);
    }
}