Codeforces Round #449 (Div. 2)

lxl大哥的珂朵莉场，被打爆了啊，掉蓝

B. Chtholly's request

题意

偶数数字回文串，求K个偶数数字回文串的和%p

分析

比赛的时候打表的打不出来啊，然后就晕了，脑子石乐志了

正解：找规律，观察可得，枚举前一半就可以了23333

 

#include <bits/stdc++.h>
#define ll long long
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define pii pair<int,int>

#define mp make_pair

using namespace std;
#define fi first
#define se second

const int maxn = 2e5+10;

int k,p;
string s;

long long answer(int x)
{
   ll sum=x;
   while(x)
   {
       sum=sum*10+x%10;
       x/=10;
       sum%=p;
   }
   return sum%p;
}

int main()
{
    scanf("%d%d", &k, &p);
    ll ans=0;
    for(int i = 1; i <= k; i++)
    {
        ans=(ans+answer(i))%p;
    }
    printf("%I64d\n", ans);
    return 0;
}

 

---

C. Nephren gives a riddle

毒瘤题

---