Codeforces Beta Round #22 (Div. 2 Only)

Codeforces Beta Round #22 (Div. 2 Only)

http://codeforces.com/contest/22

A

水题

 #include<bits/stdc++.h>
 using namespace std;
 #define lson l,mid,rt<<1
 #define rson mid+1,r,rt<<1|1
 #define sqr(x) ((x)*(x))
 #define maxn 500005
 typedef long long ll;
 /*#ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
 #endif */

 int a;
 vector<int>ve;

 int main(){
     #ifndef ONLINE_JUDGE
        // freopen("1.txt","r",stdin);
     #endif
     std::ios::sync_with_stdio(false);
     int n;
     cin>>n;
     for(int i=;i<n;i++){
         cin>>a;
         ve.push_back(a);
     }
     sort(ve.begin(),ve.end());
     ve.erase(unique(ve.begin(),ve.end()),ve.end());
     if(ve.size()==) cout<<"NO"<<endl;
     else cout<<ve[]<<endl;

 }

B

DP，有点像二维差分

 #include<bits/stdc++.h>
 using namespace std;
 #define lson l,mid,rt<<1
 #define rson mid+1,r,rt<<1|1
 #define sqr(x) ((x)*(x))
 #define maxn 500005
 typedef long long ll;
 /*#ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
 #endif */

 int n,m;
 char str[][];
 int dp[][];

 int main(){
     #ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
     #endif
     std::ios::sync_with_stdio(false);
     scanf("%d %d",&n,&m);
     int ans=;
     for(int i=;i<=n;i++) scanf("%s%*c",str[i]+);
     for(int i=;i<=n;i++){
         for(int j=;j<=m;j++){
             if(str[i][j]==''){
                 dp[i][j]++;
             }
             dp[i][j]+=dp[i-][j]+dp[i][j-]-dp[i-][j-];
         }
     }
     for(int i=;i<=n;i++){
         for(int j=;j<=m;j++){
             if(str[i][j]==''){
                 for(int k=i-;k>=;k--){
                     for(int l=j-;l>=;l--){
                         int tmp=dp[i][j]-dp[k][j]-dp[i][l]+dp[k][l];
                         if(!tmp){
                             ans=max(ans,*(i-k+j-l));
                         }
                         if(str[i][l]=='') break;
                     }
                     if(str[k][j]=='') break;
                 }
             }
         }
     }

     cout<<ans<<endl;
 }

C

构造题

 #include<bits/stdc++.h>
 using namespace std;
 #define lson l,mid,rt<<1
 #define rson mid+1,r,rt<<1|1
 #define sqr(x) ((x)*(x))
 #define maxn 500005
 typedef long long ll;
 /*#ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
 #endif */

 int n,m,v;

 int main(){
     #ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
     #endif
     std::ios::sync_with_stdio(false);
     cin>>n>>m>>v;
     if(m<n-||m>((n-)*(n-))/+n-) cout<<-<<endl;
     else if(n<) cout<<"1 2"<<endl;
     else{
         int u=v-;
         if(v==) u=;
         for(int i = ; i <= n; i++){
             if(i != v)
                 cout<<i<<" "<<v<<endl;
         }
         m -= (n - );
         for(int i = ; i <= n && m; i++){
             if(i == v || i == u) continue;
             for(int j = i + ; j <= n && m; j++){
                 if(j == v || j == u) continue;
                 cout<<i<<" "<<j<<endl;
                 m--;
             }
         }
     }

 }

D

贪心

 #include<bits/stdc++.h>
 using namespace std;
 #define lson l,mid,rt<<1
 #define rson mid+1,r,rt<<1|1
 #define sqr(x) ((x)*(x))
 #define maxn 500005
 typedef long long ll;
 /*#ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
 #endif */

 int n;
 vector<pair<int,int> >ve;
 vector<int>V;

 int main(){
     #ifndef ONLINE_JUDGE
   //      freopen("1.txt","r",stdin);
     #endif
     std::ios::sync_with_stdio(false);
     cin>>n;
     int a,b;
     for(int i=;i<=n;i++){
         cin>>a>>b;
         if(a>b) swap(a,b);
         ve.push_back(make_pair(a,b));
     }
     sort(ve.begin(),ve.end());
     int ans=;
     int r=ve[].second;
     for(int i=;i<ve.size();i++){
         if(ve[i].first>r){
             ans++;
             V.push_back(r);
             r=ve[i].second;
         }
         else{
             r=min(r,ve[i].second);
         }
     }
     V.push_back(r);
     cout<<ans<<endl;
     for(int i=;i<V.size();i++){
         cout<<V[i]<<' ';
     }
 }

E

构造强连通分量，先找到出度为0的点，跑dfs找出链或环上的头尾节点，然后把这些节点相连即可

注意，可能存在自环，所以要判断一下

 #include<bits/stdc++.h>
 using namespace std;
 #define lson l,mid,rt<<1
 #define rson mid+1,r,rt<<1|1
 #define sqr(x) ((x)*(x))
 #define maxn 500005
 typedef long long ll;
 /*#ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
 #endif */

 vector<int>ve[],head,last;
 int d[];
 int vis[];

 int dfs(int pos){
     vis[pos]=;
     if(!vis[ve[pos][]]){
         return vis[pos]=dfs(ve[pos][]);
     }
     return vis[pos]=pos;
 }

 int main(){
     #ifndef ONLINE_JUDGE
   //      freopen("1.txt","r",stdin);
     #endif
     std::ios::sync_with_stdio(false);
     int n;
     cin>>n;
     int a;
     for(int i=;i<=n;i++){
         cin>>a;
         ve[i].push_back(a);
         d[a]++;
     }
     int k=;
     for(int i=;i<=n;i++){
         if(!d[i]){
             k++;
             head.push_back(i);
             last.push_back(dfs(i));
         }
     }
     int kk=k;
     for(int i=;i<=n;i++){
         if(!vis[i]){
             k++;
             head.push_back(i);
             last.push_back(dfs(i));
         }
     }
     if(k==&&!kk) k=;
     cout<<k<<endl;
     for(int i=;i<k;i++){
         cout<<last[i]<<" "<<head[(i+)%k]<<endl;
     }
 }