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=0;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()==1) cout<<"NO"<<endl;
    else cout<<ve[1]<<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[35][35];
int dp[35][35];

int main(){
    #ifndef ONLINE_JUDGE
        freopen("1.txt","r",stdin);
    #endif
    std::ios::sync_with_stdio(false);
    scanf("%d %d",&n,&m);
    int ans=0;
    for(int i=1;i<=n;i++) scanf("%s%*c",str[i]+1);
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            if(str[i][j]=='1'){
                dp[i][j]++;
            }
            dp[i][j]+=dp[i-1][j]+dp[i][j-1]-dp[i-1][j-1];
        }
    }
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            if(str[i][j]=='0'){
                for(int k=i-1;k>=0;k--){
                    for(int l=j-1;l>=0;l--){
                        int tmp=dp[i][j]-dp[k][j]-dp[i][l]+dp[k][l];
                        if(!tmp){
                            ans=max(ans,2*(i-k+j-l));
                        }
                        if(str[i][l]=='1') break;
                    }
                    if(str[k][j]=='1') 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-1||m>((n-2)*(n-3))/2+n-1) cout<<-1<<endl;
    else if(n<3) cout<<"1 2"<<endl;
    else{
        int u=v-1;
        if(v==1) u=2;
        for(int i = 1; i <= n; i++){
            if(i != v)
                cout<<i<<" "<<v<<endl;
        }
        m -= (n - 1);
        for(int i = 1; i <= n && m; i++){
            if(i == v || i == u) continue;
            for(int j = i + 1; 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=1;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=1;
    int r=ve[0].second;
    for(int i=1;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=0;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[100005],head,last;
int d[100005];
int vis[100005];

int dfs(int pos){
    vis[pos]=1;
    if(!vis[ve[pos][0]]){
        return vis[pos]=dfs(ve[pos][0]);
    }
    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=1;i<=n;i++){
        cin>>a;
        ve[i].push_back(a);
        d[a]++;
    }
    int k=0;
    for(int i=1;i<=n;i++){
        if(!d[i]){
            k++;
            head.push_back(i);
            last.push_back(dfs(i));
        }
    }
    int kk=k;
    for(int i=1;i<=n;i++){
        if(!vis[i]){
            k++;
            head.push_back(i);
            last.push_back(dfs(i));
        }
    }
    if(k==1&&!kk) k=0;
    cout<<k<<endl;
    for(int i=0;i<k;i++){
        cout<<last[i]<<" "<<head[(i+1)%k]<<endl;
    }
}