题解 | #二叉树的前序遍历#
二叉树的前序遍历
https://www.nowcoder.com/practice/5e2135f4d2b14eb8a5b06fab4c938635
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 {
private List<Integer> res = new ArrayList<>();
/**
* 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 int[] preorderTraversal (TreeNode root) {
// write code here
preOrder(root);
return res.stream().mapToInt(Integer::intValue).toArray();
}
private void preOrder(TreeNode root) {
if (root == null) {
return;
}
res.add(root.val);
preOrder(root.left);
preOrder(root.right);
}
}
