C++

$\color{gold}{— > 蓝桥杯辅导课题解}$

思路：

模拟

$枚举年份，月份和天数直接通过年份构造出来，然后通过check-valid函数判断是否合法即可$

$时间复杂度：O(10^4)$

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

int days[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

bool check_valid(int date) {
    int year = date / 10000;
    int month = date % 10000 / 100;
    int day = date % 100;

    if (month == 0 || month > 12) return false;
    if (day == 0 || month != 2 && day > days[month]) return false;

    if (month == 2) {
        int leap = year % 400 == 0 || year % 4 == 0 && year % 100 != 0;
        if (day > days[month] + leap) return false;
    }
    return true;
}

int main() {
    int date1, date2;
    cin >> date1 >> date2;

    int res = 0;
    for (int i = 1000; i < 10000; i ++) {
        int date = i, x = i;
        for (int j = 0; j < 4; j ++) date = date * 10 + x % 10, x /= 10; // 构造日期

        if (date1 <= date && date <= date2 && check_valid(date)) res ++;
    }

    cout << res;

    return 0;
}

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