C++实现1、先序遍历的顺序建立二叉树。 2、计算二叉树的深度。 3、统计二叉树中节点的个数。

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1、C++实现先序遍历的顺序建立二叉树：

#include <iostream>
using namespace std;

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

TreeNode* buildTree() {
    int val;
    cin >> val;
    if (val == -1) {
        return NULL;
    }
    TreeNode* root = new TreeNode(val);
    root->left = buildTree();
    root->right = buildTree();
    return root;
}

void preOrder(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    cout << root->val << " ";
    preOrder(root->left);
    preOrder(root->right);
}

int main() {
    cout << "请输入先序遍历序列（-1表示空节点）：" << endl;
    TreeNode* root = buildTree();
    cout << "先序遍历结果为：" << endl;
    preOrder(root);
    return 0;
}

2、C++实现计算二叉树的深度：

#include <iostream>
#include <algorithm>
using namespace std;

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

int maxDepth(TreeNode* root) {
    if (root == NULL) {
        return 0;
    }
    int leftDepth = maxDepth(root->left);
    int rightDepth = maxDepth(root->right);
    return max(leftDepth, rightDepth) + 1;
}

int main() {
    cout << "请输入先序遍历序列（-1表示空节点）：" << endl;
    TreeNode* root = buildTree();
    int depth = maxDepth(root);
    cout << "二叉树的深度为：" << depth << endl;
    return 0;
}

3、C++实现统计二叉树中节点的个数：

#include <iostream>
using namespace std;

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

int countNodes(TreeNode* root) {
    if (root == NULL) {
        return 0;
    }
    int leftCount = countNodes(root->left);
    int rightCount = countNodes(root->right);
    return leftCount + rightCount + 1;
}

int main() {
    cout << "请输入先序遍历序列（-1表示空节点）：" << endl;
    TreeNode* root = buildTree();
    int count = countNodes(root);
    cout << "二叉树中节点的个数为：" << count << endl;
    return 0;
}