Codeforces Beta Round #29 (Div. 2, Codeforces format)

Codeforces Beta Round #29 (Div. 2, Codeforces format)

http://codeforces.com/contest/29

A

 #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 pb push_back
 #define maxn 1000005
 typedef long long ll;
 typedef unsigned long long ull;
 const ull MOD=;
 /*#ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
 #endif */

 int main(){
     #ifndef ONLINE_JUDGE
       //  freopen("1.txt","r",stdin);
     #endif
     std::ios::sync_with_stdio(false);
     int n;
     cin>>n;
     int a[],b[];
     for(int i=;i<=n;i++){
         cin>>a[i]>>b[i];
     }
     int flag=;
     for(int i=;i<=n;i++){
         for(int j=;j<=n;j++){
             if(i!=j){
                 if(a[i]+b[i]==a[j]&&a[j]+b[j]==a[i]){
                     flag=;
                 }
             }
         }
     }
     if(flag) cout<<"YES"<<endl;
     else cout<<"NO"<<endl;
 }

B

模拟

 #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 pb push_back
 #define maxn 1000005
 typedef long long ll;
 typedef unsigned long long ull;
 const ull MOD=;
 /*#ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
 #endif */

 int main(){
     #ifndef ONLINE_JUDGE
       //  freopen("1.txt","r",stdin);
     #endif
     std::ios::sync_with_stdio(false);
     double l,d,v,g,r;
     cin>>l>>d>>v>>g>>r;
     double ans=;
     if(v*g>d) ans=l/v;
     else{
         l-=d;
         double t=d/v;
         ans=t;
         double tt=g+r;
         int flag=;
         while(t>=){
             t-=g;
             if(t>=){
                 t-=r;
             }
             if(t<) flag=;
         }
       //  cout<<t<<endl;
         if(flag==){
             ans-=t;
         }
         ans+=l/v;
     }
     printf("%.7f\n",ans);
 }

C

找出一个度为1的点，然后跑dfs。因为值为1e9，所以需要离散化

 #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 pb push_back
 #define maxn 1000005
 typedef long long ll;
 typedef unsigned long long ull;
 const ull MOD=;
 /*#ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
 #endif */

 int n;
 vector<int>ve;
 int a[];
 int b[];
 int d[];
 vector<int>V[];

 int getid(int x){
     return lower_bound(ve.begin(),ve.end(),x)-ve.begin()+;
 }

 void dfs(int pos,int pre){
     cout<<ve[pos-]<<" ";
     for(int i=;i<V[pos].size();i++){
         if(V[pos][i]!=pre){
             dfs(V[pos][i],pos);
         }
     }
 }

 int main(){
     #ifndef ONLINE_JUDGE
       //  freopen("1.txt","r",stdin);
     #endif
     std::ios::sync_with_stdio(false);
     cin>>n;
     for(int i=;i<=n;i++){
         cin>>a[i]>>b[i];
         ve.pb(a[i]);
         ve.pb(b[i]);
     }
     sort(ve.begin(),ve.end());
     ve.erase(unique(ve.begin(),ve.end()),ve.end());
     int pos,pos1,pos2;
     for(int i=;i<=n;i++){
         pos1=getid(a[i]);
         pos2=getid(b[i]);
         d[pos1]++,d[pos2]++;
         V[pos1].pb(pos2);
         V[pos2].pb(pos1);
     }
     for(int i=;i<=n;i++){
         pos1=getid(a[i]);
         pos2=getid(b[i]);
         if(d[pos1]==){
             pos=pos1;
             break;
         }
         if(d[pos2]==){
             pos=pos2;
             break;
         }
     }
     dfs(pos,);
 }

D

跑两个叶子结点的最短路，看看最后的个数是不是2*n-1

 #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 pb push_back
 #define maxn 1000005
 typedef long long ll;
 typedef unsigned long long ull;
 const ull MOD=;
 /*#ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
 #endif */

 int n;
 vector<int>ve[];
 int vis[];
 int d[];
 vector<int>ans;

 void dfs(int pos,int pre,int last,vector<int>tmp){
     vis[pos]=;
     if(pre!=) {
         tmp.pb(pos);
     }
     if(pos==last){
         for(int i=;i<tmp.size();i++){
             ans.pb(tmp[i]);
         }
         return;
     }
     for(int i=;i<ve[pos].size();i++){
         if(!vis[ve[pos][i]]&&ve[pos][i]!=pre){
             dfs(ve[pos][i],pos,last,tmp);
         }
     }
 }

 int main(){
     #ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
     #endif
     std::ios::sync_with_stdio(false);
     cin>>n;
     int u,v;
     for(int i=;i<n;i++){
         cin>>u>>v;
         ve[u].pb(v);
         ve[v].pb(u);
         d[u]++,d[v]++;
     }
     int co=;
     for(int i=;i<=n;i++){
         if(d[i]==){
             co++;
         }
     }
     vector<int>son;
     son.pb();
     for(int i=;i<=co;i++){
         cin>>u;
         son.pb(u);
     }
     son.pb();
     ans.pb();
     for(int i=;i<son.size()-;i++){
         memset(vis,,sizeof(vis));
         vector<int>tmp;
         tmp.clear();
         dfs(son[i],,son[i+],tmp);
     }
     if(ans.size()==*n-){
         for(int i=;i<ans.size();i++){
             cout<<ans[i]<<" ";
         }
         cout<<endl;
     }
     else{
         cout<<-<<endl;
     }
 }

E

bfs搜索，思路很有趣

标记是用A和B的相对位置进行标记的，懂了这一点这题就解决了

 #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 pb push_back
 #define maxn 1000005
 typedef long long ll;
 typedef unsigned long long ull;
 /*#ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
 #endif */
 int n,m;
 vector<int>ve[];
 int pre[][][];
 bool book[][];
 vector<int>ans[];

 bool bfs(){
     pre[][n][]=-;
     pair<int,int>p,pp;
     p=make_pair(,n);
     queue<pair<int,int> >Q;
     Q.push(p);
     while(!Q.empty()&&pre[n][][]==){
         p=Q.front();
         Q.pop();
         int p1=p.first,p2=p.second;
         for(int i=;i<ve[p1].size();i++){
             if(!book[ve[p1][i]][p2]){
                 book[ve[p1][i]][p2]=;
                 for(int j=;j<ve[p2].size();j++){
                     if(ve[p1][i]!=ve[p2][j]){
                         if(pre[ve[p1][i]][ve[p2][j]][]==){
                             pre[ve[p1][i]][ve[p2][j]][]=p1;
                             pre[ve[p1][i]][ve[p2][j]][]=p2;
                             pp=make_pair(ve[p1][i],ve[p2][j]);
                             Q.push(pp);
                         }
                     }
                 }
             }
         }
     }
     if(pre[n][][]==) return false;
     int x=n,y=,z;
     while(x>){
         ans[].pb(x);
         ans[].pb(y);
         z=x;
         x=pre[x][y][];
         y=pre[z][y][];
     }
     return true;
 }

 int main(){
     #ifndef ONLINE_JUDGE
         freopen("1.txt","r",stdin);
     #endif
     std::ios::sync_with_stdio(false);
     cin>>n>>m;
     int u,v;
     for(int i=;i<=m;i++){
         cin>>u>>v;
         ve[u].pb(v);
         ve[v].pb(u);
     }
     if(bfs()){
         cout<<ans[].size()-<<endl;
         for(int i=;i<;i++){
             for(int j=ans[i].size()-;j>=;j--){
                 cout<<ans[i][j]<<" ";
             }
             cout<<endl;
         }
     }
     else{
         cout<<-<<endl;
     }

 }