模拟

思路：从1年1月1日开始遍历，依次判断是否到了下一月、下一年，统计从1年1月1日到询问日期所过天数。

months = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
month_name = {"January": 1, "February": 2, "March": 3, "April": 4,
              "May": 5, "June": 6, "July": 7, "August": 8,
              "September": 9, "October": 10,  "November": 11, "December": 12}
weeks = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]

def is_leap(year):
    return (year % 4 == 0 and year % 100 != 0) or year % 400 == 0  # 是否是闰年

def get_days(year, month):
    s = months[month]
    if month == 2:
        return s + is_leap(year)
    return s

while True:
    try:
        d, m, y = input().split()
        d = int(d)
        m = str(m)
        y = int(y)

        month = month_name[m]
        days = 0
        i, j, k = 1, 1, 1  # year, month, day
        while i < y or j < month or k < d:
            k += 1
            days += 1
            if k > get_days(i, j):  # 到了下个月
                k = 1
                j += 1
                if j > 12:  # 跨年
                    j = 1
                    i += 1
        print(weeks[days % 7])

    except EOFError:
        break

公式

思路：
基姆拉尔森计算公式(Kim larsen calculation formula)
W= (d+2m+3(m+1)/5+y+y/4-y/100+y/400+1)%7
w表示星期，w的取值范围是0~6，0代表星期日，1~6星期一到星期六
把一月和二月看成是上一年的十三月和十四月，例：如果是2004-1-10则换算成：2003-13-10来代入公式计算。
参考链接：https://baike.baidu.com/item/%E5%9F%BA%E5%A7%86%E6%8B%89%E5%B0%94%E6%A3%AE%E8%AE%A1%E7%AE%97%E5%85%AC%E5%BC%8F

months = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
month_name = {"January": 1, "February": 2, "March": 3, "April": 4,
              "May": 5, "June": 6, "July": 7, "August": 8,
              "September": 9, "October": 10,  "November": 11, "December": 12}
weeks = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]

while True:
    try:
        d, m, y = input().split()
        d = int(d)
        m = str(m)
        y = int(y)

        month = month_name[m]
        if month == 1 or month == 2:
            month += 12
            y -= 1 

        w = (d + 2 * month + 3 * (month + 1) // 5 + y + y // 4 - y // 100 + y // 400 + 1) % 7
        print(weeks[w])

    except EOFError:
        break