BM23 二叉树的前序遍历

https://www.nowcoder.com/practice/5e2135f4d2b14eb8a5b06fab4c938635?tpId=295&tqId=2291302&ru=/exam/oj&qru=/ta/format-top101/question-ranking&sourceUrl=%2Fexam%2Foj%3Fpage%3D1%26tab%3D%25E7%25AE%2597%25E6%25B3%2595%25E7%25AF%2587%26topicId%3D295

使用切片slice模拟栈stack，利用 stack[:len(stack)-1] 模拟pop操作

前序遍历最简单，访问顺序：当前节点->左节点->右节点

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 {
    // write code here
    rc := root
    stack := make([]*TreeNode,0,100)
    result := make([]int,0,100)
    for rc != nil || len(stack) > 0{
        if rc == nil{
            rc = stack[len(stack)-1]
            stack = stack[:len(stack)-1]
        }
        if rc.Right != nil{
            stack = append(stack,rc.Right)
        }
        result = append(result,rc.Val)
        rc = rc.Left
    }
    return result

}

C++

/**
 * struct TreeNode {
 * int val;
 * struct TreeNode *left;
 * struct TreeNode *right;
 * TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
 /**
 * 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vector
 */
 vector<int> preorderTraversal(TreeNode* root) {
 // write code here
 TreeNode* rc = root;
 stack<TreeNode*> st;
 vector<int> res;
 while(rc != nullptr || st.size() > 0){
 if(rc == nullptr){
 rc = st.top();
 st.pop();
 }
 if(rc->right != nullptr){
 st.push(rc->right);
 }
 res.push_back(rc->val);
 rc = rc->left; 
 }
 return res;
 }
};