Codeforces Beta Round #22 (Div. 2 Only)

Posted 2021-02-08 fighting-sh

Codeforces Beta Round #22 (Div. 2 Only)

http://codeforces.com/contest/22

A

水题

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define lson l,mid,rt<<1
 4 #define rson mid+1,r,rt<<1|1
 5 #define sqr(x) ((x)*(x))
 6 #define maxn 500005
 7 typedef long long ll;
 8 /*#ifndef ONLINE_JUDGE
 9         freopen("1.txt","r",stdin);
10 #endif */
11 
12 int a;
13 vector<int>ve;
14 
15 int main(){
16     #ifndef ONLINE_JUDGE
17        // freopen("1.txt","r",stdin);
18     #endif
19     std::ios::sync_with_stdio(false);
20     int n;
21     cin>>n;
22     for(int i=0;i<n;i++){
23         cin>>a;
24         ve.push_back(a);
25     }
26     sort(ve.begin(),ve.end());
27     ve.erase(unique(ve.begin(),ve.end()),ve.end());
28     if(ve.size()==1) cout<<"NO"<<endl;
29     else cout<<ve[1]<<endl;
30     
31 }

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B

DP，有点像二维差分

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define lson l,mid,rt<<1
 4 #define rson mid+1,r,rt<<1|1
 5 #define sqr(x) ((x)*(x))
 6 #define maxn 500005
 7 typedef long long ll;
 8 /*#ifndef ONLINE_JUDGE
 9         freopen("1.txt","r",stdin);
10 #endif */
11 
12 int n,m;
13 char str[35][35];
14 int dp[35][35];
15 
16 int main(){
17     #ifndef ONLINE_JUDGE
18         freopen("1.txt","r",stdin);
19     #endif
20     std::ios::sync_with_stdio(false);
21     scanf("%d %d",&n,&m);
22     int ans=0;
23     for(int i=1;i<=n;i++) scanf("%s%*c",str[i]+1);
24     for(int i=1;i<=n;i++){
25         for(int j=1;j<=m;j++){
26             if(str[i][j]==‘1‘){
27                 dp[i][j]++;
28             }
29             dp[i][j]+=dp[i-1][j]+dp[i][j-1]-dp[i-1][j-1];
30         }
31     }
32     for(int i=1;i<=n;i++){
33         for(int j=1;j<=m;j++){
34             if(str[i][j]==‘0‘){
35                 for(int k=i-1;k>=0;k--){
36                     for(int l=j-1;l>=0;l--){
37                         int tmp=dp[i][j]-dp[k][j]-dp[i][l]+dp[k][l];
38                         if(!tmp){
39                             ans=max(ans,2*(i-k+j-l));
40                         }
41                         if(str[i][l]==‘1‘) break;
42                     }
43                     if(str[k][j]==‘1‘) break;
44                 }
45             }
46         }
47     }
48 
49 
50     cout<<ans<<endl;
51 }

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C

构造题

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define lson l,mid,rt<<1
 4 #define rson mid+1,r,rt<<1|1
 5 #define sqr(x) ((x)*(x))
 6 #define maxn 500005
 7 typedef long long ll;
 8 /*#ifndef ONLINE_JUDGE
 9         freopen("1.txt","r",stdin);
10 #endif */
11 
12 int n,m,v;
13 
14 int main(){
15     #ifndef ONLINE_JUDGE
16         freopen("1.txt","r",stdin);
17     #endif
18     std::ios::sync_with_stdio(false);
19     cin>>n>>m>>v;
20     if(m<n-1||m>((n-2)*(n-3))/2+n-1) cout<<-1<<endl;
21     else if(n<3) cout<<"1 2"<<endl;
22     else{
23         int u=v-1;
24         if(v==1) u=2;
25         for(int i = 1; i <= n; i++){
26             if(i != v)
27                 cout<<i<<" "<<v<<endl;
28         }
29         m -= (n - 1);
30         for(int i = 1; i <= n && m; i++){
31             if(i == v || i == u) continue;
32             for(int j = i + 1; j <= n && m; j++){
33                 if(j == v || j == u) continue;
34                 cout<<i<<" "<<j<<endl;
35                 m--;
36             }
37         }
38     }
39 
40 }

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D

贪心

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define lson l,mid,rt<<1
 4 #define rson mid+1,r,rt<<1|1
 5 #define sqr(x) ((x)*(x))
 6 #define maxn 500005
 7 typedef long long ll;
 8 /*#ifndef ONLINE_JUDGE
 9         freopen("1.txt","r",stdin);
10 #endif */
11 
12 int n;
13 vector<pair<int,int> >ve;
14 vector<int>V;
15 
16 int main(){
17     #ifndef ONLINE_JUDGE
18   //      freopen("1.txt","r",stdin);
19     #endif
20     std::ios::sync_with_stdio(false);
21     cin>>n;
22     int a,b;
23     for(int i=1;i<=n;i++){
24         cin>>a>>b;
25         if(a>b) swap(a,b);
26         ve.push_back(make_pair(a,b));
27     }
28     sort(ve.begin(),ve.end());
29     int ans=1;
30     int r=ve[0].second;
31     for(int i=1;i<ve.size();i++){
32         if(ve[i].first>r){
33             ans++;
34             V.push_back(r);
35             r=ve[i].second;
36         }
37         else{
38             r=min(r,ve[i].second);
39         }
40     }
41     V.push_back(r);
42     cout<<ans<<endl;
43     for(int i=0;i<V.size();i++){
44         cout<<V[i]<<‘ ‘;
45     }
46 }

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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

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define lson l,mid,rt<<1
 4 #define rson mid+1,r,rt<<1|1
 5 #define sqr(x) ((x)*(x))
 6 #define maxn 500005
 7 typedef long long ll;
 8 /*#ifndef ONLINE_JUDGE
 9         freopen("1.txt","r",stdin);
10 #endif */
11 
12 vector<int>ve[100005],head,last;
13 int d[100005];
14 int vis[100005];
15 
16 int dfs(int pos){
17     vis[pos]=1;
18     if(!vis[ve[pos][0]]){
19         return vis[pos]=dfs(ve[pos][0]);
20     }
21     return vis[pos]=pos;
22 }
23 
24 int main(){
25     #ifndef ONLINE_JUDGE
26   //      freopen("1.txt","r",stdin);
27     #endif
28     std::ios::sync_with_stdio(false);
29     int n;
30     cin>>n;
31     int a;
32     for(int i=1;i<=n;i++){
33         cin>>a;
34         ve[i].push_back(a);
35         d[a]++;
36     }
37     int k=0;
38     for(int i=1;i<=n;i++){
39         if(!d[i]){
40             k++;
41             head.push_back(i);
42             last.push_back(dfs(i));
43         }
44     }
45     int kk=k;
46     for(int i=1;i<=n;i++){
47         if(!vis[i]){
48             k++;
49             head.push_back(i);
50             last.push_back(dfs(i));
51         }
52     }
53     if(k==1&&!kk) k=0;
54     cout<<k<<endl;
55     for(int i=0;i<k;i++){
56         cout<<last[i]<<" "<<head[(i+1)%k]<<endl;
57     }
58 }

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