codeforces 690C3 Brain Network
simple:并查集一下
#include <vector> #include <iostream> #include <queue> #include <cmath> #include <map> #include <cstring> #include <algorithm> #include <cstdio> using namespace std; typedef long long LL; const int N=2e5+5; const LL mod=1e9+7; int fa[N]; int find(int x){ return x==fa[x]?x:fa[x]=find(fa[x]); } int main(){ int n,m; scanf("%d%d",&n,&m); for(int i=1;i<=n;++i)fa[i]=i; while(m--){ int u,v; scanf("%d%d",&u,&v); u=find(u),v=find(v); if(u!=v)fa[u]=v,--n; else{printf("no\n");return 0;} } if(n==1)printf("yes\n"); else printf("no\n"); return 0; }
medium:最长路
#include <vector> #include <iostream> #include <queue> #include <cmath> #include <map> #include <cstring> #include <algorithm> #include <cstdio> using namespace std; typedef long long LL; const int N=2e5+5; const LL mod=1e9+7; int head[N],tot,n,m,d[N>>1],ret; struct Edge{ int v,next; }edge[N]; void add(int u,int v){ edge[tot].v=v; edge[tot].next=head[u]; head[u]=tot++; } void bfs(int u){ memset(d,-1,sizeof(d)); queue<int>q;q.push(u); d[u]=0; while(!q.empty()){ int x=q.front(); q.pop(); for(int i=head[x];~i;i=edge[i].next){ int v=edge[i].v; if(d[v]!=-1)continue; d[v]=d[x]+1; q.push(v); if(d[v]>d[ret])ret=v; } } } int main(){ scanf("%d%d",&n,&m); memset(head,-1,sizeof(head));tot=0; for(int i=1;i<n;++i){ int u,v; scanf("%d%d",&u,&v); add(u,v);add(v,u); } ret=1; bfs(1);bfs(ret); printf("%d\n",d[ret]); return 0; }
hard:动态最长路,LCA维护
#include <vector> #include <iostream> #include <queue> #include <cmath> #include <map> #include <cstring> #include <algorithm> #include <cstdio> using namespace std; typedef long long LL; const int N=2e5+5; const LL mod=1e9+7; int head[N],tot,n,d[N]; struct Edge{ int v,next; }edge[N]; void add(int u,int v){ edge[tot].v=v; edge[tot].next=head[u]; head[u]=tot++; } int fa[N][20]; void dfs(int u,int f){ fa[u][0]=f;d[u]=d[f]+1; for(int i=head[u];~i;i=edge[i].next)dfs(edge[i].v,u); } int LCA(int u,int v){ if(d[u]<d[v])swap(u,v); for(int t=d[u]-d[v],i=0;t;t>>=1,++i) if(t&1)u=fa[u][i]; if(u==v)return u; for(int i=19;i>=0;--i){ if(fa[u][i]!=-1&&fa[u][i]!=fa[v][i]) u=fa[u][i],v=fa[v][i]; } return fa[u][0]; } int main(){ scanf("%d",&n); memset(head,-1,sizeof(head)); for(int i=2;i<=n;++i){ int u;scanf("%d",&u);add(u,i); } memset(fa,-1,sizeof(fa)); dfs(1,0);fa[1][0]=-1; for(int j=1;(1<<j)<=n;++j) for(int i=1;i<=n;++i) if(fa[i][j-1]!=-1) fa[i][j]=fa[fa[i][j-1]][j-1]; printf("1"); int x=1,y=2,z=1; for(int i=3;i<=n;++i){ int tpx=LCA(x,i),lenx=d[x]+d[i]-2*d[tpx]; int tpy=LCA(y,i),leny=d[y]+d[i]-2*d[tpy]; if(lenx>=leny&&lenx>=z){ y=i;z=lenx; } else if(leny>=lenx&&leny>=z){ x=i;z=leny; } printf(" %d",z); } printf("\n"); return 0; }