[dfs树] Codeforces 521E #295 (Div. 1) E. Cycling City

来源：互联网发布：excel编程实现整行数据编辑：程序博客网时间：2024/05/16 15:09

这个东西啊题解里讲的太复杂了直接发现充要条件的两个环有公共部分那么我们瞎JB dfs以下就好了

但是这个东西啊输方案真是蛋疼我弄来弄去搞了好久就是写不出优雅的代码

#include<cstdio>  #include<cstdlib>  #include<algorithm>  #include<cstring>  #define cl(x) memset(x,0,sizeof(x))  using namespace std;    inline char nc(){    static char buf[100000],*p1=buf,*p2=buf;    if (p1==p2) { p2=(p1=buf)+fread(buf,1,100000,stdin); if (p1==p2) return EOF; }    return *p1++;  }    inline void read(int &x){    char c=nc(),b=1;    for (;!(c>='0' && c<='9');c=nc()) if (c=='-') b=-1;    for (x=0;c>='0' && c<='9';x=x*10+c-'0',c=nc()); x*=b;  }    const int N=200005;    struct edge{    int u,v,next;  }G[N<<1];  int head[N],inum=1;    inline void add(int u,int v,int p){    G[p].u=u; G[p].v=v; G[p].next=head[u]; head[u]=p;  }int n,m;int au,av,flag;int depth[N],fat[N],tag[N];#define V G[p].vint sta[N];inline void dfs(int u,int fa){  sta[++*sta]=u;  for (int p=head[u];p;p=G[p].next)    if (p!=(fa^1)){      if (!depth[V])fat[V]=u,depth[V]=depth[u]+1,dfs(V,p),tag[u]+=tag[V];      else if (depth[V]<depth[u])tag[u]++,tag[V]--;    }  if (tag[u]>=2)    flag=1,au=G[fa].u,av=G[fa].v;}int instack[N];int cir1,cir2;int lst1[N],lst2[N];int in1[N],in2[N];inline void find(int u,int fa){  instack[u]=1;  for (int p=head[u];p;p=G[p].next)    if (p!=(fa^1)){      if (!depth[V])depth[V]=depth[u]+1,find(V,p);      else if (depth[V]<depth[u]){if (instack[au] && instack[av] && depth[V]<=depth[au] && depth[V]<=depth[av]){  if (!cir1){    cir1=p;    int t=u; while (depth[t]>=depth[V]) in1[t]=1,lst1[++*lst1]=t,t=fat[t];  }  else if (!cir2){    cir2=p;    int t=u; while (depth[t]>=depth[V]) in2[t]=1,lst2[++*lst2]=t,t=fat[t];  }}      }    }  instack[u]=0;}int pnt,lst[N];inline void Print(){  printf("%d",pnt);  for (int i=1;i<=pnt;i++)    printf(" %d",lst[i]);  printf("\n");}int main(){  int iu,iv;  int u1,v1,u2,v2;  freopen("t.in","r",stdin);  freopen("t.out","w",stdout);  read(n); read(m);  for (int i=1;i<=m;i++)    read(iu),read(iv),add(iu,iv,++inum),add(iv,iu,++inum);  for (int r=1;r<=n;r++)    if (!depth[r]){      *sta=0; *lst1=0; *lst2=0; cir1=0; cir2=0; flag=0;      depth[r]=1;      dfs(r,0);      if (!flag)continue;      for (int i=1;i<=*sta;i++) depth[sta[i]]=0; depth[r]=1;      find(r,0);      au=0,av=0;      for (int i=1;i<=*sta;i++)if (in1[sta[i]] && in2[sta[i]]){  if (!au || depth[au]>depth[sta[i]])    au=sta[i];  if (!av || depth[av]<depth[sta[i]])    av=sta[i];}      printf("YES\n");        pnt=0;      for (int i=av;depth[i]>=depth[au];i=fat[i]) lst[++pnt]=i;      Print();      int pos1,pos2;        for (int i=1;i<=*lst1;i++)if (lst1[i]==au) pos1=i; else if (lst1[i]==av) pos2=i;      pnt=0;      for (int i=pos2;i!=pos1;i=i==1?*lst1:i-1)lst[++pnt]=lst1[i];      lst[++pnt]=lst1[pos1];      Print();        for (int i=1;i<=*lst2;i++)if (lst2[i]==au) pos1=i; else if (lst2[i]==av) pos2=i;      pnt=0;      for (int i=pos2;i!=pos1;i=i==1?*lst2:i-1)lst[++pnt]=lst2[i];      lst[++pnt]=lst2[pos1];      Print();      return 0;    }  printf("NO\n");  return 0;}

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