Luogu P5022 旅行 搜索+贪心

好吧。。。一直咕。。现在才过。。。被卡常卡到爆。。。

写的垃圾版本，$n^2$无脑删边。。可以发现走出来的是棵树。。。更优秀的及数据加强版先咕着。。。一定写。qwq

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<vector>
#define ll long long
#define R register int
static char B[<<],*S=B,*D=B;
#define getchar() (S==D&&(D=(S=B)+fread(B,1,1<<15,stdin),S==D)?EOF:*S++)
using namespace std;
inline int g() {
    R ret=,fix=; register char ch; while(!isdigit(ch=getchar())) fix=ch=='-'?-:fix;
    do ret=ret*+(ch^); while(isdigit(ch=getchar())); return ret*fix;
} int n,m,tot;
int ans[]; bool vis[],used[][];
int w[][];
inline void dfs1(int u) { vis[u]=true; ans[++tot]=u;
    for(R i=,lim=w[u][];i<=lim;++i) { R v=w[u][i];
        if(!vis[v]) dfs1(v);
    }
} int s[]; int U,V;
pair<int,int> e[];
inline void dfs2(int u) { vis[u]=true; s[++tot]=u;
    for(R i=,lim=w[u][];i<=lim;++i) { R v=w[u][i];
        if((u==U&&v==V)||(u==V&&v==U)) continue;
        if(!vis[v]) dfs2(v);
    }
}
inline bool ck() {for(R i=;i<=n;++i) if(s[i]!=ans[i]) return ans[i]>s[i];  return false;}
signed main() {
    n=g(),m=g(); for(R i=,u,v;i<=m;++i) u=g(),v=g(),w[u][++w[u][]]=v,w[v][++w[v][]]=u,e[i]=make_pair(u,v);
    for(R i=;i<=n;++i) sort(w[i]+,w[i]+w[i][]+);
    if(m==n-) {
        dfs1(); for(R i=;i<=n;++i) printf("%d ",ans[i]);
    } else {
        for(R i=;i<=n;++i) ans[i]=n-i+;
        for(R i=;i<=m;++i) {
            tot=; memset(vis,,sizeof(vis)); U=e[i].first,V=e[i].second;
            dfs2(); if(tot==n&&ck()) memcpy(ans,s,sizeof(s));
        } for(R i=;i<=n;++i) printf("%d ",ans[i]);
    }
}

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2019.06.04