a = int(input()) #获取年份
b = int((a % 4 == 0 and a % 100 != 0) or a % 400 == 0)+28 #计算二月长度
print([-1,31,b,31,30,31,30,31,31,30,31,30,31][int(input())])
#从得到的这年月份长度数组（部分打表）中抽取相关月并直接输出

过于暴力，不建议参考此答案。

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
    int year,leap,month;cin>>year>>month;
    if(year%4==0&&year%100!=0||year%400==0)
        leap=1;
    else
        leap=0;
    int a[13]={31,28+leap,31,30,31,30,31,31,30,31,30,31};
    int i=month;
    if(i)
        cout<<a[i-1];
    return 0;
}

#python3

a=float(input())
b=float(input())
if b==1:
    print(31)
elif b==3:
    print(31)
elif b==4:
    print(30)
elif b==5:
    print(31)
elif b==6:
    print(30)
elif b==7:
    print(31)
elif b==8:
    print(31)
elif b==9:
    print(30)
elif b==10:
    print(31)
elif b==11:
    print(30)
elif b==12:
    print(31)
elif b==2:
    if a%4==0 and a%100!=0:
        print(29)
    elif a%400==0:
        print(29)
    else:
        print(28)

y=int(input())
m=int(input())
if m==1 or m==3 or m==5 or m==7 or m==8 or m==10 or m==12:
c=31
elif m==2:
c=28
else:
c=30
if y%100==0:
if y%400==0 and m==2:
c=29
elif y%4==0 and m==2 :
c=29
print(int(c))

x=float(input())
y=float(input())
if y in [1,3,5,7,8,10,12]:  print(31)
elif y in [4,6,9,11]: print(30)
elif y==2 and x%400==0: print(29)
elif y==2 and x%4==0 and x%100!=0: print(29)
else: print(28)

中规中矩

#include <bits/stdc++.h>
using namespace std;
int v[13]={31,28,31,30,31,30,31,31,30,31,30,31};
int main()
{
int a,b;
cin>>a>>b;
if(a%4==0&&b==2&&a%100!=0||a%400==0&&b==2)
{
cout<<29;
return 0;
}
cout<<v[b-1];
return 0;
}

#include <bits/stdc++.h>
using namespace std;
int main()
{
int year,month, leap, day;
cin>>year>>month;
int r4=year%4;
int r100=year%100;
int r400=year%400;
if(r4==0)
if(r100==0)
if(r400==0)
leap=1;
else
leap=0;

else
leap=1;
else
leap=0;

if(month==1 || month==3 || month==5 || month==7 || month==8 || month==10 || month==12)
day=31;
else
if(month==2)
day=28+leap;
else
day=30;
cout<<day<<endl;
return 0;
}

有那么点累赘。。

a=int(input())
b=int(input())
if((b==1)or(b==3)or(b==5)or(b==7)or(b==8)or(b==10)or(b==12)):
print("31")
elif(b==2):
if(((a%100!=0)and(a%4==0))or((a%100==0)and(a%400==0))):
print("29")
else:
print("28")
else:
print("30")