c语言，设计一个算法，求二叉树第k层的结点个数。完整代码

以下是C语言设计的算法，用于求二叉树第k层的结点个数：

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

struct node{
    struct node *left;
    struct node *right;
    int value;
};

int countNodesAtLevelK(struct node *root, int k){
    if(root == NULL){
        return 0;
    }
    else if(k == 1){
        return 1;
    }
    else{
        return countNodesAtLevelK(root->left, k-1) + countNodesAtLevelK(root->right, k-1);
    }
}

int main(){
    struct node *root = (struct node*)malloc(sizeof(struct node));
    root->value = 1;

    root->left = (struct node*)malloc(sizeof(struct node));
    root->left->value = 2;

    root->right = (struct node*)malloc(sizeof(struct node));
    root->right->value = 3;

    root->left->left = (struct node*)malloc(sizeof(struct node));
    root->left->left->value = 4;

    root->left->right = (struct node*)malloc(sizeof(struct node));
    root->left->right->value = 5;

    root->right->left = (struct node*)malloc(sizeof(struct node));
    root->right->left->value = 6;

    root->right->right = (struct node*)malloc(sizeof(struct node));
    root->right->right->value = 7;

    int k = 3;
    int count = countNodesAtLevelK(root, k);
    printf("The number of nodes at level %d is %d", k, count);

    return 0;
}

在此示例中，我们创建了一个二叉树，并求出了第三层的结点数。请注意，此算法使用递归来计算二叉树的层级结点数，因此效率可能不高。