//隐藏条件就是1年1月1日是星期一，把这个时间点设为锚点
//计算输入的日期与锚点之间隔了多少天
//天数对7取余，所得结果就是星期几
#include <cstdio>
#include <cstring>

int month[13][2]={
    {0,0},{31,31},{28,29},{31,31},{30,30},{31,31},{30,30},{31,31},{31,31},
    {30,30},{31,31},{30,30},{31,31}
};
char month_name[13][20]={
    "","January","February","March","April","May","June","July","August",
    "September","October","November","December"
};
char week_name[7][20]={
    "Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"
};
bool isLeap(int year){
    return (year%4==0&&year%100!=0)||(year%400==0);
}
int main(){
    int d,m,y;
    char s[20];
    while(scanf("%d%s%d",&d,s,&y)!=EOF){
        for(m=1;m<=12;m++){
            if(strcmp(s,month_name[m])==0) break;
        }
        int y1=1,m1=1,d1=1,day=1;
        while(y1<y||m1<m||d1<d){
            d1++;
            if(d1==month[m1][isLeap(y1)]+1){
                d1=1;
                m1++;
            }
            if(m1==13){
                m1=1;
                y1++;
            }
            day++;
        }
        printf("%s\n",week_name[day%7]);
    }
    return 0;
}

Python四行代码，利用datetime库。

import datetime
while True:
    try:
        month = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October',
                 'November', 'December']
        week = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]
        d, m, y = input().split()
        print(week[int(datetime.datetime(int(y), month.index(m) + 1, int(d)).strftime("%w"))])
    except:
        break

看了下面的答案后，发现还可以更简单，"A"直接输出的是Tuesday这种格式，太方便了。于是代码可以缩成三行：

import datetime
while True:
    try:
        month = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October','November', 'December']
        d, m, y = input().split()
        print((datetime.datetime(int(y), month.index(m) + 1, int(d)).strftime("%A")))
    except:
        break

人生苦短，我爱python。

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <vector>
#include <map>
#include <cmath>
#include <set>
#include <queue>
 
using namespace std;
map<string, int> mp;
map<int,string> _mp;
string months[] = {"","January","February","March","April","May","June","July","August","September","October","November","December"};
string weekdays[] = {"","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday"};
void init()
{
    for(int i = 1;i<=12;i++)
    {
        mp[months[i]] = i;
    }
    for(int i = 1 ;i<=7;i++)
    _mp[i] = weekdays[i]; 
}
int main()
{
    int d,y;
    string m;
    init();
    while(cin >> d >> m >> y)
    {
        int mm = mp[m];
        if(mm == 1 || mm == 2)
        {
            mm += 12;
            y--;
        }
        int ans = (d+2*mm+3*(mm+1)/5+y+y/4-y/100+y/400)%7 + 1;
        cout << _mp[ans] << endl;
    }
}

import datetime
print datetime.datetime.strptime(raw_input(), "%d %B %Y").strftime("%A")

Python其实只要两行233

// java
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
import java.util.*;

public class Main {
    public static void main(String[] args) {
        Map<Object, Object> map = new HashMap<>();
        map.put("January", 1);
        map.put("February", 2);
        map.put("March", 3);
        map.put("April", 4);
        map.put("May", 5);
        map.put("June", 6);
        map.put("July", 7);
        map.put("August", 8);
        map.put("September", 9);
        map.put("October", 10);
        map.put("November", 11);
        map.put("December", 12);

        map.put(7, "Sunday");
        map.put(1, "Monday");
        map.put(2, "Tuesday");
        map.put(3, "Wednesday");
        map.put(4, "Thursday");
        map.put(5, "Friday");
        map.put(6, "Saturday");

        Scanner input = new Scanner(System.in);
        String[] split = input.nextLine().split(" ");
        int day = Integer.parseInt(split[0]);
        int month = (int) map.get(split[1]);
        int year = Integer.parseInt(split[2]);
        LocalDate date = LocalDate.of(year, month, day);
        DayOfWeek ofWeek = date.getDayOfWeek();

        System.out.println(map.get(ofWeek.getValue()));
    }
}

// c++
#include<bits/stdc++.h>
using namespace std;
bool isLeapYear(int year) {
    return (year % 400 == 0) || (year % 4 == 0 && year % 100 != 0);
}

int daysOfYear(int year) {
    if(isLeapYear(year)) return 366;
    return 365;
}


int daytab[2][13] = {
    {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
    {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
};

vector<string> months = {"January","February","March","April","May","June","July","August","September","October","November","December"};
vector<string> weekdays = {"Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday"};

int main() {
    int year, month, day;
    //char monthStr[20];
    string monthStr;
    //scanf("%2d %s %4d", &day, monthStr, &year);
    while( cin >> day >> monthStr >> year) {
        //cout << day << monthStr << year;
        for(int i = 0; i < months.size(); i++) {
            if(monthStr == months[i]) {
               month = i;
               break;
            }
        }
        int y = year;
        long long allDay = 0;
        // 计算从公元1年1月1号到当前的天数
        for(int i = 1; i < year; i++) {
            allDay += daysOfYear(i);
        }
        for(int i = 0; i <= month; i++) {
            allDay += daytab[isLeapYear(year)][i];
        }
        allDay += day - 1;
        cout << weekdays[allDay % 7] << endl;
    }
}

//王道机试指南解法
#include<iostream>
#include<cstring>
#define ISLEAP(x)  (x%4==0&&x%100!=0)||x%400==0?1:0
int YofM[13][2] = {
    0,0,31,31,28,29,31,31,30,30,31,31,30,30,
    31,31,31,31,30,30,31,31,30,30,31,31
};
struct Data {
    int data;
    int month;
    int year;
    Data() {
        data = 1; month = 0; year = 0;
    }
    void nextdata() {
        data++;
        if (data>YofM[month][ISLEAP(year)]) {
            month++; data = 1;
            if (month>12)
            {
                year++; month = 1;
            }
        }//if
    }
};
char monthName[13][20] = {
    "","January","February","March","April","May","June","July",
    "August","September","October","November","December"
};
char weekName[7][20] = {
    "Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"
};
int Daycount[3001][13][32];
int main() {
    Data D;
    int num = 0;
    while (D.year <= 3000) {
        Daycount[D.year][D.month][D.data] = num;
        D.nextdata();
        num++;
    }//while
    int d, m, y;
    char s[20];
    while (std::cin >> d >> s >> y) {
        for (m = 1; m<13; m++) {
            if (strcmp(s, monthName[m]) == 0) { break; }
        }//for
        int i = Daycount[y][m][d] - Daycount[2018][2][25];
        std::cout << weekName[(i % 7 + 7) % 7];
    }//while
    return 0;
}

#include<iostream>
#include<stdio.h>
#include<string.h>
using namespace std;
char  mon[][20]={" ","January","February","March","April","May","June","July","August","September","October","November","December"};
char  week[][20]={"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"};
int day[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
bool leap(int y){
  if(y%400==0||(y%4==0&&y%100!=0))return true;
  else return false;
}
int days(int y,int m,int d){
  int sum=0;
  for(int i=1;i<y;++i){
    if(leap(i))sum+=366;
    else sum+=365;
    }
  if(leap(y))day[2]=29;
  else day[2]=28;
  for(int j=1;j<m;++j){
    sum+=day[j];
  }
  sum+=d;
  return sum;
}
int main(){
  int y,m,d;
  char month[20];

  while(cin>>d>>month>>y){
    for(int i=1;i<13;++i){

        if(strcmp(month,mon[i])==0){
           m=i;
           break;
        }
    }
    int cnt1=days(y,m,d);
    int cnt2=days(2018,3,7);
    int del=cnt1-cnt2;
    del=del%7;
    cout<<week[(del+3)%7];
  }
  return 0;
}

	

#include<stdio.h>
#include<string.h>
#define ISYEAR(x) x%100!=0&&x%4==0||x%400==0?1:0
int dateOfMonth[13][2]={
    0,0,
    31,31,
    28,29,
    31,31,
    30,30,
    31,31,
    30,30,
    31,31,
    31,31,
    30,30,
    31,31,
    30,30,
    31,31
};
struct Date{
    int Year;
    int Month;
    int Day;
    void NextDay(){
        Day++;
        if(Day>dateOfMonth[Month][ISYEAR(Year)]){
            Day=1;
            Month++;
            if(Month>12){
                Month=1;
                Year++;
            }
        }
    }
};
int buf[3001][13][32];
char MonthName[13][20]={
    " ",
    "January",
    "February",
    "March",
    "April",
    "May",
    "June",
    "July",
    "August",
    "September",
    "October",
    "November",
    "December"
};
char WeekName[7][20]={
    "Sunday", 
    "Monday",
    "Tuesday",
    "Wednesday",
    "Thursday",
    "Friday",
    "Saturday"
};
int main(){
    Date tmp;
    tmp.Year=0;
    tmp.Month=1;
    tmp.Day=1;
    int cnt=0;
    while(tmp.Year!=3001){
        buf[tmp.Year][tmp.Month][tmp.Day]=cnt;
        tmp.NextDay();
        cnt++;
    }
    int d,m,y;
    char s[20];
    while(scanf("%d%s%d",&d,s,&y)!=EOF){
        for(m=1;m<13;m++){
            if(strcmp(MonthName[m],s)==0)
                break;
        }
    }
    int days=(buf[y][m][d]-buf[2012][7][16])+1;
    printf("%s",WeekName[(days%7+7)%7]);    
}

from datetime import datetime
Month = {'May': 5, 'December': 12, 'October': 10, 'August': 8,
         'July': 7, 'February': 2, 'January': 1, 'September': 9,
         'March': 3, 'April': 4, 'November': 11, 'June': 6}
try:
    while 1:
        k = raw_input().split()
        print datetime(int(k[2]),Month[k[1]],int(k[0])).strftime('%A').capitalize()
except:
    pass

//#include<cstdio>
#include<iostream>
#include<string>
#include "map"
using namespace std;
bool isLeap(int year)
{
    bool k=year%400==0||year%100!=0&&year%4==0;
    return k;
}
int main()
{
    map<string,int> mymap={
            {"January",1},{"February",2},
            {"March",3},{"April",4},
            {"May",5},{"June",6},
            {"July",7},{"August",8},
            {"September",9}, {"October",10},
            {"November",11},{"December",12}
            };
    map<int,string >keymap={
            {1,"Monday"},{2,"Tuesday"},
            {3,"Wednesday"},{4,"Thursday"},
            {5,"Friday"},{6,"Saturday"},
            {0,"Sunday"}
    };
    int maday[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
    char str[10];
    string month;
    int day,year;
    int weekday;
    while(cin >> day >> month >> year)
    {


        int n=0;
        for(int i=1;i<year;i++)
        {
            if(isLeap(i))
            {
                n+=366;
            }
            else {

                n += 365;
            }
        }
        if(isLeap(year))
        {
            maday[2]=29;
        }
        else
        {
            maday[2]=28;
        }
        int m=mymap[month];
        for(int i=1;i<=m;i++)
        {
            n+=maday[i-1];
        }
        n+=day;
        weekday=n%7;
       cout<<keymap[weekday]<<endl;


    }
    return 0;
}摸着大佬的思想

#include <array>
#include <iostream>
#include <string>
using namespace std;

const array<string, 13>months = {   //月份名
    "",
    "January",
    "February",
    "March",
    "April",
    "May",
    "June",
    "July",
    "August",
    "September",
    "October",
    "November",
    "December"
};

const array<string, 7>dayOfWeek = { //星期名
    "Sunday",
    "Monday",
    "Tuesday",
    "Wednesday",
    "Thursday",
    "Friday",
    "Saturday"
};

inline bool isLeapYear(int year) {  //判断是否是闰年
    return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
}

class Date {
  private:
    int year, month, day;   //年月日
    int totalDays;          //该日期是从公元元年1月1日开始的第多少天
  public:
    Date(int day, const string& month, int year);   //构造函数
    string getDayOfWeek();  //判断星期几（隐含条件：公元元年1月1日是星期一）
};

Date::Date(int day, const string& month, int year): day(day), year(year) {
    for (int i = 1; i <= 12; i++) {
        if (months[i] == month) {
            this->month = i;
            break;
        }
    }
    int years = year - 1;
    totalDays = years * 365 + years / 4 - years / 100 + years / 400;
    for (int month = 1; month < this->month; month++) {
        switch (month) {
            case 1:
            case 3:
            case 5:
            case 7:
            case 8:
            case 10:
            case 12:
                totalDays += 31;
                break;
            case 2:
                totalDays += 28 + isLeapYear(year);
                break;
            default:
                totalDays += 30;
        }
    }
    totalDays += day;
}

string Date::getDayOfWeek() {
    return dayOfWeek[totalDays % 7];
}

int main() {
    int day, year;
    string month;
    while (cin >> day >> month >> year) {
        cout << Date(day, month, year).getDayOfWeek() << endl;
    }
    return 0;
}

#include <iostream>
#include <string>
#include <map>
using namespace std;
bool isLeapYear(int year){
	 return year%400==0||year%4==0&&year%100!=0;
}
int main(){
	int days[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
	map<string,int> monthToint={
		{"January",1},
		{"February",2},
		{"March",3},
		{"April",4},
		{"May",5},
		{"June",6},
		{"July",7},
		{"August",8},
		{"September",9},
		{"October",10},
		{"November",11},
		{"December",12},
	};
	int year,mon,day;
	char str[10]; 
	string month;
	while(scanf("%d%s%d",&day,str,&year)!=EOF){
		month=str;
		mon=monthToint[month];
		int sum=0;
		int i=year,j=mon,k=day;
		int left;
		if(i<2024){
			while(1){
				if(isLeapYear(i)){
					days[2]=29;		
				}else{
					days[2]=28;	
				}
				k++;
				sum++;
				if(k>days[j]){
					++j;
					k=1;
					if(j>12){
						j=1;
						++i;
					}
				}
				if(i==2024&&j==1&&k==13){
					break;
				}
			}
			left=sum%7;
			switch(left){
				case 0: cout<<"Saturday"<<endl;break;	
				case 1: cout<<"Friday"<<endl; break;
				case 2: cout<<"Thursday"<<endl;break;
				case 3: cout<<"Wednesday"<<endl;break;
				case 4: cout<<"Tuesday"<<endl;break;
				case 5: cout<<"Monday"<<endl;break;
				case 6: cout<<"Sunday"<<endl;break;
			}
		}else if(year==2024&&mon==1&&day<13){
			while(1){
				if(isLeapYear(i)){
					days[2]=29;		
				}else{
					days[2]=28;	
				}
				k++;
				sum++;
				if(k>days[j]){
					++j;
					k=1;
					if(j>12){
						j=1;
						++i;
					}
				}
				if(i==2024&&j==1&&k==13){
					break;
				}
			}
			left=sum%7;
			switch(left){
				case 0: cout<<"Saturday"<<endl;break;	
				case 1: cout<<"Friday"<<endl; break;
				case 2: cout<<"Thursday"<<endl;break;
				case 3: cout<<"Wednesday"<<endl;break;
				case 4: cout<<"Tuesday"<<endl;break;
				case 5: cout<<"Monday"<<endl;break;
				case 6: cout<<"Sunday"<<endl;break;
			}
		}else{ //2024-1-13 2024-1-15
			while(1){
				if(isLeapYear(i)){
					days[2]=29;		
				}else{
					days[2]=28;	
				}
				--k;
				sum++;
				if(k==0){
					--j;
					if(j<1){
						j=12;
						--i;
					} 
					k=days[j];
				}
				if(i==2024&&j==1&&k==13){
					break;
				}
			}
			left=sum%7;
			switch(left){
				case 0: cout<<"Saturday"<<endl;break;	
				case 1: cout<<"Sunday"<<endl; break;
				case 2: cout<<"Monday"<<endl;break;
				case 3: cout<<"Tuesday"<<endl;break;
				case 4: cout<<"Wednesday"<<endl;break;
				case 5: cout<<"Thursday"<<endl;break;
				case 6: cout<<"Friday"<<endl;break;
			}
		}
	} 
	return 0;
}