用c++完成二叉树的先序创建

可以按照以下步骤来完成二叉树的先序创建：

1. 定义二叉树结构体：

struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

2. 定义一个函数来创建二叉树：

struct TreeNode* createTree() {
    int val;
    scanf("%d", &val);
    if (val == -1) { // 如果输入的值为 -1，表示该节点为空
        return NULL;
    }
    struct TreeNode* node = (struct TreeNode*) malloc(sizeof(struct TreeNode));
    node->val = val;
    node->left = createTree(); // 递归创建左子树
    node->right = createTree(); // 递归创建右子树
    return node;
}

3. 在主函数中调用该函数来创建二叉树：

int main() {
    struct TreeNode* root = createTree();
    // ...
    return 0;
}

完整代码如下：

#include <stdio.h>
#include <stdlib.h>

struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

struct TreeNode* createTree() {
    int val;
    scanf("%d", &val);
    if (val == -1) {
        return NULL;
    }
    struct TreeNode* node = (struct TreeNode*) malloc(sizeof(struct TreeNode));
    node->val = val;
    node->left = createTree();
    node->right = createTree();
    return node;
}

int main() {
    struct TreeNode* root = createTree();
    // ...
    return 0;
}