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#yyds干货盘点# 面试必刷TOP101：二叉树的前序遍历
source link: https://blog.51cto.com/u_15488507/5582439
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#yyds干货盘点# 面试必刷TOP101：二叉树的前序遍历
精选 原创1.简述：
描述给你二叉树的根节点 root ，返回它节点值的 前序 遍历。
数据范围：二叉树的节点数量满足 ，二叉树节点的值满足 ，树的各节点的值各不相同
{1,#,2,3}
[1,2,3]
2.代码实现：
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 int[] preorderTraversal (TreeNode root) {
// write code here
List<Integer> list = new ArrayList<>();
handTree(root, list);
int[] arr = new int[list.size()];
int i = 0;
for(int v : list){
arr[i++] = v;
}
return arr;
}
private void handTree(TreeNode root, List<Integer> list){
if(root != null){
list.add(root.val);
handTree(root.left, list);
handTree(root.right, list);
}
}
}
/*
* 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 int[] preorderTraversal (TreeNode root) {
// write code here
List<Integer> list = new ArrayList<>();
handTree(root, list);
int[] arr = new int[list.size()];
int i = 0;
for(int v : list){
arr[i++] = v;
}
return arr;
}
private void handTree(TreeNode root, List<Integer> list){
if(root != null){
list.add(root.val);
handTree(root.left, list);
handTree(root.right, list);
}
}
}
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