bzoj1293: [SCOI2009]生日礼物

#include<cstdio>
#include<cstring>
#include<cctype>
#include<algorithm>
using namespace std;
#define rep(i,s,t) for(register int i=s;i<=t;i++)
#define dwn(i,s,t) for(register int i=s;i>=t;i--)
#define clr(x,c) memset(x,c,sizeof(x))
int read(){
    int x=0;char c=getchar();
    while(!isdigit(c)) c=getchar();
    while(isdigit(c)) x=x*10+c-‘0‘,c=getchar();
    return x;
}
const int nmax=1e6+5;
const int inf=0x7f7f7f7f;
struct nd{
    int a,b;
    bool operator<(const nd&rhs)const {
      return b<rhs.b;}
};
nd ns[nmax];
int t[71];
void mins(int &a,int b){
    if(a>b) a=b;
}
int main(){
    int n=read(),m=read(),u,cnt=0;
    rep(i,1,m){
        u=read();
        rep(j,1,u) ns[++cnt].b=read(),ns[cnt].a=i;
    }
    sort(ns+1,ns+n+1);
    //rep(i,1,n) printf("%d %d\n",ns[i].a,ns[i].b);
    int r=0,ans=inf;cnt=0;
    rep(i,1,n){
        if(i!=1) if(!--t[ns[i-1].a]) cnt--;
        while(cnt<m){
            if(++r>n) break;
            if(++t[ns[r].a]==1) cnt++;
        }
        if(cnt!=m) break;
        mins(ans,ns[r].b-ns[i].b);
        //printf("%d %d %d %d\n",i,r,ns[i].b,ns[r].b);
    }
    printf("%d\n",ans);
    return 0;
}