LeetCode 144. Binary Tree Preorder Traversal 解题报告

144. Binary Tree Preorder Traversal

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Question

Total Accepted: 108336 Total
Submissions: 278322 Difficulty: Medium

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].

Note: Recursive solution is trivial, could you do it iteratively?

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求一棵二叉树的先根遍历序。题目说了，递归的解法十分简单，能否用非递归的方式求解。

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我的AC代码

public class BinaryTreePreorderTraversal {

	public List<Integer> preorderTraversal(TreeNode root) {
        List<Integer> list = new ArrayList<Integer>();
        Stack<TreeNode> stack = new Stack<TreeNode>();
        TreeNode cur = root;
        while (cur != null || !stack.isEmpty()) {
			while (cur != null) {
				list.add(cur.val);
				if(cur.right != null) stack.add(cur.right);
				cur = cur.left;
			}
			if(!stack.isEmpty()) cur = stack.pop();
		}
        return list;
    }
}