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
     */
    int node = -1;
    public void PreOrder(TreeNode b,int[] arr){
        if(b != null){
            node +=1;
            arr[node] = b.val;
            PreOrder(b.left,arr);
            PreOrder(b.right,arr);
        }
    }

    public int[] preorderTraversal (TreeNode root) {
        // write code here
        int[] arr = new int[101];
        PreOrder(root,arr);
        int[] ans = new int [node+1];
        int j =0;
        for(int i:arr){
            if(i == 0){
                break;
            }
            ans[j] = i;
            j+=1;
        }
        return ans;
    }
}