Educational Codeforces Round 63 (Rated for Div. 2)(A,B,C,D)

题目链接:http://codeforces.com/contest/1155

第一题(模拟)

#include
using namespace std;

#define debug puts("YES");
#define rep(x,y,z) for(int (x)=(y);(x)<(z);(x)++)
#define ll long long

#define lrt int l,int r,int rt
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define root l,r,rt
#define mst(a,b) memset((a),(b),sizeof(a))
#define pii pair
#define fi first
#define se second
#define mk(x,y) make_pair(x,y)
const int mod=1e9+7;
const int maxn=5e2+10;
const int ub=1e6;
ll powmod(ll x,ll y){ll t; for(t=1;y;y>>=1,x=x*x%mod) if(y&1) t=t*x%mod; return t;}
int gcd(int x,int y){
    if(y==0) return x;
    return gcd(y,x%y);
}

string s;
int n;

int main(){
    cin>>n>>s;
    int flag=0,l,r;
    ///int len=s.size();
    for(int i=0;is[i+1]){
            l=i,r=i+1;
            flag=1;
            break;
        }
    }
    if(flag==0) puts("NO");
    else {
        puts("YES");
        cout<

第二题(博弈+模拟)

#include
using namespace std;

#define debug puts("YES");
#define rep(x,y,z) for(int (x)=(y);(x)<(z);(x)++)
#define ll long long

#define lrt int l,int r,int rt
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define root l,r,rt
#define mst(a,b) memset((a),(b),sizeof(a))
#define pii pair
#define fi first
#define se second
#define mk(x,y) make_pair(x,y)
const int mod=1e9+7;
const int maxn=5e2+10;
const int ub=1e6;
ll powmod(ll x,ll y){ll t; for(t=1;y;y>>=1,x=x*x%mod) if(y&1) t=t*x%mod; return t;}
int gcd(int x,int y){
    if(y==0) return x;
    return gcd(y,x%y);
}
int flag=0,n;
string s;
int main(){
    cin>>n>>s;
    int cnt=(n-11)/2,stp=cnt;
    for(int i=0;istp) isw=0;
                break;
            }
        }
        if(isw) puts("YES");
        else puts("NO");
    }

    return 0;
}

第三题(数论)

#include
using namespace std;

#define debug puts("YES");
#define rep(x,y,z) for(int (x)=(y);(x)<(z);(x)++)
#define ll long long

#define lrt int l,int r,int rt
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define root l,r,rt
#define mst(a,b) memset((a),(b),sizeof(a))
#define pii pair
#define fi first
#define se second
#define mk(x,y) make_pair(x,y)
const int mod=1e9+7;
const int maxn=3e5+10;
const int ub=1e6;
ll powmod(ll x,ll y){ll t; for(t=1;y;y>>=1,x=x*x%mod) if(y&1) t=t*x%mod; return t;}
ll gcd(ll x,ll y){
    if(y==0) return x;
    return gcd(y,x%y);
}
ll n,m;
ll a[maxn],b[maxn];
int main(){
    cin>>n>>m;
    ll gd=0;
    rep(i,0,n){
        cin>>a[i];
        ///gd1=gcd(gd1,a[i]);
        if(i) gd=gcd(gd,a[i]-a[i-1]);
    }
    int flag=0,res=0,pos=0;
    rep(i,0,m){
        cin>>b[i];
        if(gd%b[i]==0){
            flag=1;
            res=i+1;
            pos=a[0];
        }
    }
    if(flag){
        puts("YES");
        cout<

 第四题(DP):

#include
using namespace std;

#define debug puts("YES");
#define rep(x,y,z) for(int (x)=(y);(x)<(z);(x)++)
#define ll long long

#define lrt int l,int r,int rt
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define root l,r,rt
#define mst(a,b) memset((a),(b),sizeof(a))
#define pii pair
#define fi first
#define se second
#define mk(x,y) make_pair(x,y)
const int mod=1e9+7;
const int maxn=3e5+100;
const int ub=1e6;
ll powmod(ll x,ll y){ll t; for(t=1;y;y>>=1,x=x*x%mod) if(y&1) t=t*x%mod; return t;}
ll gcd(ll x,ll y){
    if(y==0) return x;
    return gcd(y,x%y);
}
ll n,x,k;
ll dp[maxn][3];
int main(){
    cin>>n>>k;
    mst(dp,0);
    ll ans=0;
    rep(i,1,n+1){
        cin>>x;
        dp[i][0]=dp[i-1][0]+x;
        dp[i][0]=max(dp[i][0],0LL);
        dp[i][1]=max(dp[i-1][1],dp[i-1][0])+x*k;
        dp[i][1]=max(dp[i][1],0LL);
        dp[i][2]=max(dp[i-1][1],dp[i-1][2])+x;
        dp[i][2]=max(dp[i][2],0LL);
        ans=max(ans,max(dp[i][2],max(dp[i][0],dp[i][1])));
    }
    cout<