题解 | #二叉树的前序遍历#

此为迭代法

using System;
using System.Collections.Generic;

/*
public class TreeNode
{
	public int val;
	public TreeNode left;
	public TreeNode right;

	public TreeNode (int x)
	{
		val = x;
	}
}
*/

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 List<int> preorderTraversal (TreeNode root) {
        List<int> result = new List<int>();
        Stack<TreeNode> st = new Stack<TreeNode>();
        TreeNode cur;
        if(root != null)st.Push(root);
        while(st.Count != 0){
            cur = st.Peek();
            if(cur != null){
                st.Pop();
                if(cur.right != null) st.Push(cur.right);
                if(cur.left != null) st.Push(cur.left);
                st.Push(cur);
                st.Push(null);
            }
            else{
                st.Pop();
                result.Add(st.Peek().val);
                st.Pop();
            }
        }
        return result;
    }
}