Codeforces round #518 Div. 1 no rollover records

A: set f [I] [J] [0/1] to the number of solutions where the first I digit is J and the second digit does not meet/has met the limit. Strong DP prefix and optimization.

#include<iostream> #include<cstdio>#include<cmath>#include<cstdlib>#include<cstring>#include<algorithm>using namespace std;int read(){    int x=0,f=1;char c=getchar();    while (c<‘0‘||c>‘9‘) {if (c==‘-‘) f=-1;c=getchar();}    while (c>=‘0‘&&c<=‘9‘) x=(x<<1)+(x<<3)+(c^48),c=getchar();    return x*f;}#define N 100010#define P 998244353#define K 200int n,a[N],f[N][K+1][2],g[N][K+1][2];//0 there is limit void inc(int &x,int y){x+=y;if (x>=P) x-=P;}int main(){#ifndef ONLINE_JUDGE    freopen("a.in","r",stdin);    freopen("a.out","w",stdout);#endif    n=read();    for (int i=1;i<=n;i++) a[i]=read();    f[0][0][0]=1;    for (int i=0;i<=K;i++) g[0][i][0]=1;    for (int i=1;i<=n;i++)    {    if (a[i]!=-1)    {        inc(f[i][a[i]][1],(g[i-1][K][1]-g[i-1][a[i]-1][1]+P)%P);        inc(f[i][a[i]][1],f[i-1][a[i]][0]);        inc(f[i][a[i]][0],g[i-1][a[i]-1][0]),inc(f[i][a[i]][0],g[i-1][a[i]-1][1]);    }    else    {        for (int j=1;j<=K;j++)        {            inc(f[i][j][1],(g[i-1][K][1]-g[i-1][j-1][1]+P)%P);            inc(f[i][j][1],f[i-1][j][0]);            inc(f[i][j][0],g[i-1][j-1][0]),inc(f[i][j][0],g[i-1][j-1][1]);        }    }    for (int j=1;j<=K;j++)    g[i][j][0]=(f[i][j][0]+g[i][j-1][0])%P,g[i][j][1]=(f[i][j][1]+g[i][j-1][1])%P;    }    if (a[n]!=-1) cout<<f[n][a[n]][1];    else    {        int ans=0;        for (int i=1;i<=200;i++) inc(ans,f[n][i][1]);        cout<<ans;    }    return 0;}

View code

B: Obviously, the valid root must be the midpoint of the diameter. Run DFS several times.

#include<iostream> #include<cstdio>#include<cmath>#include<cstdlib>#include<cstring>#include<algorithm>using namespace std;int read(){    int x=0,f=1;char c=getchar();    while (c<‘0‘||c>‘9‘) {if (c==‘-‘) f=-1;c=getchar();}    while (c>=‘0‘&&c<=‘9‘) x=(x<<1)+(x<<3)+(c^48),c=getchar();    return x*f;}#define N 100010int n,m,p[N],deep[N],fa[N],t=0,root;struct data{int to,nxt;}edge[N<<1];void addedge(int x,int y){t++;edge[t].to=y,edge[t].nxt=p[x],p[x]=t;}void dfs(int k){    for (int i=p[k];i;i=edge[i].nxt)    if (edge[i].to!=fa[k])    {        deep[edge[i].to]=deep[k]+1;        fa[edge[i].to]=k;        dfs(edge[i].to);    }}bool check(int k){    bool flag=1;    int x=0;    for (int i=p[k];i;i=edge[i].nxt)    if (edge[i].to!=fa[k]) x++;    if (x==0) return deep[k]==m;    if (x>=3)    {        for (int i=p[k];i;i=edge[i].nxt)        if (edge[i].to!=fa[k]) flag=flag&&check(edge[i].to);    }    else flag=0;    return flag;}int main(){#ifndef ONLINE_JUDGE    freopen("b.in","r",stdin);    freopen("b.out","w",stdout);#endif    n=read(),m=read();    for (int i=1;i<n;i++)    {        int x=read(),y=read();        addedge(x,y),addedge(y,x);    }    dfs(1);    for (int i=1;i<=n;i++) if (deep[i]>=deep[root]) root=i;    memset(deep,0,sizeof(deep));    memset(fa,0,sizeof(fa));    dfs(root);    for (int i=1;i<=n;i++) if (deep[i]>=deep[root]) root=i;    if (deep[root]!=m*2) {cout<<"No";return 0;}    for (int i=1;i<=m;i++) root=fa[root];    memset(deep,0,sizeof(deep));    memset(fa,0,sizeof(fa));    dfs(root);    if (check(root)) cout<<"Yes";    else cout<<"No";    return 0;}

View code

20 min is very friendly. Then, the structure of C is discarded. D. No. E. Hack does not move. Over an hour, I watched the rankings go down.

Why is the speed faster?

Result: rank 95 rating + 83 suddenly becomes yellow, and it feels like the next one will fall back.

 

Codeforces round #518 Div. 1 no rollover records