要修改代码，比较月日距离现在远近的方法，可以使用日期库来处理日期并进行比较。以下是修改后的代码：
#include <iostream>#include <string>#include <vector>#include <algorithm>#include <chrono> // 添加日期库#include <ctime>struct Purchase {std::string date;std::string product;double price;};bool compareDates(const Purchase& p1, const Purchase& p2) {// 使用日期库计算日期差值std::tm t1 = {}, t2 = {};strptime(p1.date.c_str(), "%Y-%m-%d", &t1);strptime(p2.date.c_str(), "%Y-%m-%d", &t2);auto timePoint1 = std::chrono::system_clock::from_time_t(std::mktime(&t1));auto timePoint2 = std::chrono::system_clock::from_time_t(std::mktime(&t2));return timePoint1 > timePoint2; // 比较时间点远近，时间点越大表示时间越早}double calculateAveragePrice(const std::vector<Purchase>& purchases, const std::string& product, int N) {double sum = 0.0;int count = 0;for (const Purchase& purchase : purchases) {if (purchase.product == product) {sum += purchase.price;count++;if (count == N) break; // 达到最近N次购买数量后退出循环}}return (count > 0) ? sum / count : 0.0; // 避免除以零的情况}int main() {int m, n;std::cin >> m >> n;std::vector<Purchase> purchases(m);for (int i = 0; i < m; i++) {std::cin >> purchases[i].date >> purchases[i].product >> purchases[i].price;}std::sort(purchases.begin(), purchases.end(), compareDates); // 按照日期远近排序double keyboardAvgPrice = calculateAveragePrice(purchases, "keyboard", n);double mouseAvgPrice = calculateAveragePrice(purchases, "mouse", n);std::cout << std::fixed;std::cout.precision(1);std::cout << keyboardAvgPrice << std::endl;std::cout << mouseAvgPrice << std::endl;return 0;}
修改后的代码通过引入日期库 <chrono> 和 <ctime> 来处理日期，并使用 strptime() 将日期字符串转换为 tm 结构，然后使用 std::chrono 库中的时间点来进行比较。请注意，以上代码仅适用于具有标准格式（如”YYYY-MM-DD”）的日期字符串。
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