用c语言给一个求二叉树内部节点的算法

以下是一个用 C 语言编写的求二叉树内部节点数量的算法：

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

// 定义二叉树结构体
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

// 计算二叉树内部节点数量的函数
int countNodes(struct TreeNode* root) {
    if (root == NULL) {
        return 0;
    }
    return countNodes(root->left) + countNodes(root->right) + 1;
}

int main() {
    // 构造一棵二叉树
    struct TreeNode* root = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->val = 1;
    root->left = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->left->val = 2;
    root->left->left = NULL;
    root->left->right = NULL;
    root->right = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->right->val = 3;
    root->right->left = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->right->left->val = 4;
    root->right->left->left = NULL;
    root->right->left->right = NULL;
    root->right->right = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->right->right->val = 5;
    root->right->right->left = NULL;
    root->right->right->right = NULL;

    // 计算二叉树内部节点数量并输出结果
    int count = countNodes(root);
    printf("Internal nodes: %d\n", count);

    // 释放二叉树内存
    free(root->left);
    free(root->right->left);
    free(root->right->right);
    free(root->right);
    free(root);

    return 0;
}

这个算法通过递归遍历二叉树，对每个节点进行计数，并返回计数的结果。对于空节点，返回 0。