反復法を用いて二叉木を前順に遍歴する--Leetcodeシリーズ(七)
Given a binary tree, return the preorder traversal of its nodes' values.
For example: Given binary tree
return
Note: Recursive solution is trivial, could you do it iteratively?
My Answer
テーマの出所:https://oj.leetcode.com/problems/binary-tree-preorder-traversal/
For example: Given binary tree
{1,#,2,3}
, 1
\
2
/
3
return
[1,2,3]
. Note: Recursive solution is trivial, could you do it iteratively?
My Answer
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List preorderTraversal(TreeNode root) {
Stack stack = new Stack();
List list = new ArrayList();
if(root == null){
return list;
}
stack.push(root);
while(!stack.empty()){
TreeNode top = stack.pop();
list.add(top.val);
if(top.right != null){
stack.push(top.right);
}
if(top.left != null){
stack.push(top.left);
}
}
return list;
}
}
テーマの出所:https://oj.leetcode.com/problems/binary-tree-preorder-traversal/