2022蓝桥杯省赛C++A组补题

题解链接

D.选数异或

题目链接

#include 
#include 
#include 
#include 
using namespace std;
#define int long long
const int N = 200010;
int Fmin[N][20];
int lg2[N];
int a[N],id[N];
int n,m,x;
vector<int>cnt[1500010];
void init_log()
{
    lg2[0]=-1;
    for(int i=1;i<N;i++)lg2[i]=lg2[i>>1]+1;
}
void init()
{
	for(int i=0;i<=n;i++)Fmin[i][0]=id[i];	
	int k=lg2[n];
	for(int j=1;j<=k;j++)
		for(int i=1;i<=n-(1<<j)+1;i++)
		{
			Fmin[i][j]=min(Fmin[i][j-1],Fmin[i+(1<<j-1)][j-1]);
		}
}
int RMQ(int l,int r)
{
	int k=lg2[r-l+1];
	int minv=min(Fmin[l][k],Fmin[r-(1<<k)+1][k]);
	return minv;
}
signed main()
{
	ios::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
	cin>>n>>m>>x;
	memset(id,0x3f,sizeof id);
	for(int i=1;i<=n;i++)
	{
		cin>>a[i];
		cnt[a[i]].push_back(i);
	}
	for(int i=1;i<=n;i++)
	{
		int t=a[i]^x;
		if(cnt[t].size()==0)continue;
		int pos=upper_bound(cnt[t].begin(),cnt[t].end(),i)-cnt[t].begin();
		if(pos==cnt[t].size())continue;
		id[i]=cnt[t][pos];
	}
	init_log();
	init();
	for(int i=0,l,r;i<m;i++)
	{
		cin>>l>>r;
		if(RMQ(l,r)<=r)cout<<"yes\n";
		else cout<<"no\n";
	}
}

E.爬树的甲壳虫—DP+概率

题目链接

#include 
#include 
#include 
#include 
using namespace std;
#define int long long
const int mod = 998244353, N = 100010;
int qmi(int a,int b){int res=1;while(b){if(b&1)res=res*a%mod;a=a*a%mod;b>>=1;}return res%mod;}
int f[N];
signed main()
{
	int n;cin>>n;
	for(int i=1,x,y;i<=n;i++)
	{
		cin>>x>>y;
		f[i]=(f[i-1]+1)*y%mod*qmi(y-x,mod-2)%mod;
	}
	cout<<f[n]<<'\n';
}

F.青蛙过河—二分+贪心

题目链接

#include 
#include 
#include 
#include 
using namespace std;
//#define int long long
const int N = 100010;
int n,x;
int a[N];
bool check(int mid)
{
	int sum=0;
	for(int i=1;i<=mid;i++)sum+=a[i];
	int minv=sum;
	for(int i=mid+1;i<n;i++)
	{
		sum=sum+a[i]-a[i-mid];
		minv=min(minv,sum);
		if(minv<2*x)return false;
	}
	return true;
}
signed main()
{
	cin>>n>>x;
	for(int i=1;i<n;i++)cin>>a[i];
	int l=1,r=n;
	while(l<r)
	{
		int mid=l+r>>1;
		if(check(mid))r=mid;
		else l=mid+1;
	}
	cout<<r<<'\n';
}

G.最长不下降子序列

题目链接