LeetCode题解：Binary Tree Preorder Traversal

Given a binary tree, return the preorder traversal of its nodes’ values.

For example:

Given binary tree {1,#,2,3},

1

\

2

/

3

return [1,2,3].

题意：先序遍历

思路：

代码：

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List<Integer> preorderTraversal(TreeNode root) {
Stack<TreeNode> rights = new Stack<TreeNode>();
List<Integer> result = new ArrayList<Integer>();

while(root != null){
result.add(root.val);

if(root.right != null){
rights.push(root.right);
}

root = root.left;

if(root == null && !rights.isEmpty()){
root = rights.pop();
}
}

return result;
}
}