题解 | #二叉树的前序遍历#

package main

import (
	. "nc_tools"
)

/*
 * type TreeNode struct {
 *   Val int
 *   Left *TreeNode
 *   Right *TreeNode
 * }
 */

/**
 * 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
 */
func preorderTraversal(root *TreeNode) []int {
	// 迭代
    if root == nil {
        return nil
    }
	result := make([]int, 0)
	stack := []*TreeNode{root}
    for len(stack) > 0 {
        node := stack[len(stack)-1]
        stack = stack[:len(stack)-1]
        result = append(result, node.Val)
        if node.Right != nil {
            stack = append(stack, node.Right)
        }
        if node.Left != nil {
            stack = append(stack, node.Left)
        }
    }


	return result
}

/** 递归
*func preorderTraversal(root *TreeNode) []int {
	// write code here
	result := make([]int, 0)
	var preorder func(node *TreeNode)
	preorder = func(node *TreeNode) {
		if node == nil {
			return
		}
		result = append(result, node.Val)
		preorder(root.Left)
		preorder(root.Right)
	}
    preorder(root)
	return result
}
*/