【HNOI2008】神奇的国度

题面

https://www.luogu.org/problem/P3196

题解

// luogu-judger-enable-o2
#include<cstdio>
#include<cstring>
#include<iostream>
#include<vector>
#define ri register int
#define N 10500
using namespace std;

inline int read() {
  int ret=0,f=0; char ch=getchar();
  while (ch<'0' || ch>'9') f|=(ch=='-'),ch=getchar();
  while (ch>='0'&& ch<='9') ret*=10,ret+=(ch-'0'),ch=getchar();
  return f?-ret:ret;
}

int n,m,s[N];
vector<int> to[N],V[N];
bool vis[N],used[N];
int a[N];
int col[N];

int main() {
  n=read(); m=read();
  for (ri i=1;i<=m;i++) {
    int a=read(),b=read();
    to[a].push_back(b); to[b].push_back(a);
  }
  for (ri i=1;i<=n;i++) V[0].push_back(i);
  int x=n;
  vis[n]=1;
  int maxs=0;
  for (ri i=1;i<=n;i++) {
    vis[x]=1;
    for (ri j=0;j<to[x].size();j++) {
      int y=to[x][j];
      if (vis[y]) continue;
      V[++s[y]].push_back(y);
      if (s[y]>maxs) maxs=s[y];
    }
    bool fl=0;
    while (maxs>=0) {
      for (ri j=V[maxs].size()-1;j>=0;j--) {
        if (vis[V[maxs][j]]) V[maxs].pop_back();
        else {x=V[maxs][j]; fl=1; break;}
      }
      if (!fl) maxs--; else break;
    }
  }
  int cnt=0;
  for (ri i=1;i<=n;i++) cnt=max(cnt,s[i]+1);
  printf("%d
",cnt);
}