66. 二叉树的前序遍历.md
描述
给出一棵二叉树,返回其节点值的前序遍历。
您在真实的面试中是否遇到过这个题?
样例
给出一棵二叉树 {1,#,2,3},
1
\
2
/
3
返回 [1,2,3]
.
Binary Tree Preorder Traversal
Description
Given a binary tree, return the preorder traversal of its nodes' values.
/**
* 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.
*/
public List<Integer> preorderTraversal(TreeNode root) {
// write your code here
List<Integer> res = new ArrayList<>();
Stack<TreeNode> lisk = new Stack<>();
if(root == null){
return res;
}
lisk.push(root);
while(!lisk.isEmpty()){
//取出后加入的:即左孩子
TreeNode temp = lisk.pop();
res.add(temp.val);
//先加入右边的
if(temp.right != null){
lisk.push(temp.right);
}
//后加入左边的
if(temp.left != null){
lisk.push(temp.left);
}
}
return res;
}
}