树的先序遍历c++代码

以下是树的先序遍历的C++代码：

#include<iostream>
using namespace std;

//定义一个树的结构体
struct TreeNode{
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x): val(x), left(NULL), right(NULL) {}
};

void preOrder(TreeNode* root){
    if(root == NULL){
        return;
    }
    cout << root->val << " ";  //输出当前节点的值
    preOrder(root->left);      //递归遍历左子树
    preOrder(root->right);     //递归遍历右子树
}

int main(){
    //构建一个二叉树
    TreeNode* root = new TreeNode(1);
    root->left = new TreeNode(2);
    root->right = new TreeNode(3);
    root->left->left = new TreeNode(4);
    root->left->right = new TreeNode(5);

    //输出先序遍历结果
    cout << "Pre-order traversal: ";
    preOrder(root);

    return 0;
}

输出结果：

Pre-order traversal: 1 2 4 5 3