A

#include<bits/stdc++.h>
using std::cin;
using std::cout;
using std::string;
typedef long long LL;
const int N=1e5+10;
int arr[N];
int main()
{
    arr[1]=arr[2]=1;
    for(int i=3;i<=100;++i)
    {
        arr[i]=arr[i-1]+arr[i-2];
        if(arr[i]>20211001)
        {
            printf("%d\n",i);
            return 0;
        }
    }
    return 0;
}

B

#include<bits/stdc++.h>
using std::cin;
using std::cout;
using std::string;
typedef long long LL;
const int N=1e5+10;
int arr[N],n,a,b;
int main()
{
    string str;
    cin>>n>>str;
    for(size_t i=0;i<str.length();++i)
    {
        if(str[i]=='A') ++a;
        else ++b;
    }
    if(a>b) printf("A\n");
    else printf("B\n");
    return 0;
}

C

#include<bits/stdc++.h>
using std::cin;
using std::cout;
using std::string;
using std::unordered_map;
typedef long long LL;
const int N=110;
int arr[N][30],n,m;
LL ans;
unordered_map<char,int>mp;
int main()
{
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;++i)
    {
        for(int j=1;j<=m;++j)
        {
            scanf("%d",&arr[i][j]);
        }
    }
    for(int i=1,j='A';i<=26;++i,++j) mp[j]=i;
    string str;
    cin>>str;
    for(int i=1;i<str.length();i+=2)
    {
        int tmpnum=0;
        char op=str[i++];
        for(int j=i;str[j]!='+'&&j<str.length();++j) tmpnum=tmpnum*10+str[j]-'0';
        ans+=arr[tmpnum][mp[op]];
    }
    printf("%d\n",ans);
    return 0;
}

D

#include<bits/stdc++.h>
using std::cin;
using std::cout;
using std::string;
using std::unordered_map;
typedef long long LL;
const int N=1e6+10;
int arr[N],n;
LL ans;
int main()
{
    scanf("%d",&n);
    unordered_map<int,int>mp;
    for(int i=1;i<=n;++i)
    {
        scanf("%d",&arr[i]);
        ++mp[arr[i]];
    }
    ans=n*(n-1)/2*(n-2)/3;
    for(auto x=mp.begin();x!=mp.end();++x)
    {
        auto y=x->second;
        //printf("ans:%d\n",ans);
        if(y>=2) 
        ans-=y*(y-1)/2*(n-y);
    }
    printf("%lld\n",ans);
    return 0;
}

E暴力

#include<bits/stdc++.h>
using std::cin;
using std::cout;
using std::string;
using std::unordered_map;
using std::next_permutation;
typedef long long LL;
const int N=15,M=1e6+10;
int arr[M][N],t[N],idx=1;
void write(int n)
{
    for(int i=1;i<=n;++i) arr[idx][i]=t[i];
    ++idx;
}
bool check(int n)
{
    int sum[30],div[30];
    memset(sum,0,sizeof sum);
    memset(div,0,sizeof div);
    for(int i=1;i<=n;++i)
    {
        ++sum[i+t[i]];
        ++div[i-t[i]+15];
        if(sum[i+t[i]]>=2||div[i-t[i]+15]>=2) return 0;
    }
    return 1;
}
void print(int wz,int n)
{
    for(int i=1;i<=n;++i) printf("%d ",arr[wz][i]);
    printf("\n");
}
bool checksame(int a,int b,int n)
{
    for(int i=1;i<=n;++i)
    {
        if(arr[a][i]==arr[b][i]) return 0;
    }
    return 1;
}
void fun(int n)
{
    for(int i=1;i<=n;++i) t[i]=i;
    do
    {
        if(check(n)) write(n);
    }while(next_permutation(t+1,t+n+1));
    int ans=0;
    for(int i=1;i<idx;++i)
    {
        for(int j=1;j<idx;++j)
        {
            if(i==j) continue;
            if(checksame(i,j,n)) ++ans;
        }
    }
    printf("%d\n",ans);
}
int main()
{
    for(int i=2;i<=11;++i)
    {
        idx=1;
        printf("i=%d:",i);
        fun(i);
    }
    return 0;
}

E正解

#include<stdio.h>
int ans[]={0,0,0,0,2,40,12,496,3252,48328,205188,2732488};
int main()
{
    int n;
    scanf("%d",&n);
    printf("%d\n",ans[n]);
    return 0;
}