TYVJ NOIP2017金秋冲刺训练营杯联赛模拟大奖赛第二轮Day2题解

#include<iostream>
#include<cstring>
#include<cstdlib>
#include<cstdio> 
#include<algorithm>
#define ll long long 
using namespace std;
const int maxn=1000010,inf=1e9;
int n,m,T;
int fac2[maxn],fac5[maxn];
void read(int &k)
{
    int f=1;k=0;char c=getchar();
    while(c<‘0‘||c>‘9‘)c==‘-‘&&(f=-1),c=getchar();
    while(c<=‘9‘&&c>=‘0‘)k=k*10+c-‘0‘,c=getchar();
    k*=f;
}
int main()
{
    freopen("zero.in","r",stdin);
    freopen("zero.out","w",stdout);
    read(T);
    for(int i=1;i<=1000000;i++)
    {
        int x=i;fac2[i]=fac2[i-1];fac5[i]=fac5[i-1];
        for(;(x&1)==0;x>>=1)fac2[i]++;
        for(;x%5==0;x/=5)fac5[i]++;
    }
    while(T--)
    {
        read(m);read(n);
        int cnt2=fac2[m]-fac2[n]-fac2[m-n];
        int cnt5=fac5[m]-fac5[n]-fac5[m-n];
        printf("%d\n",min(cnt2,cnt5));
    }
    return 0;
}

#include<iostream>
#include<cstring>
#include<cstdlib>
#include<cstdio> 
#include<algorithm>
#define ll long long 
using namespace std;
const int maxn=500010,inf=1e9;
struct poi{int too,pre;}e[maxn];
int n,m,x,y,z,tot,ans,st,ed,cnt,len;
int mx1[maxn],mx2[maxn],d[maxn],last[maxn],isrt[maxn],rt[maxn],q[maxn];
void read(int &k)
{
    int f=1;k=0;char c=getchar();
    while(c<‘0‘||c>‘9‘)c==‘-‘&&(f=-1),c=getchar();
    while(c<=‘9‘&&c>=‘0‘)k=k*10+c-‘0‘,c=getchar();
    k*=f;
}
inline void add(int x,int y){e[++tot].too=y;e[tot].pre=last[x];last[x]=tot;}
void dfs(int x,int fa)
{
    d[x]=d[fa]+1;mx1[x]=d[x];mx2[x]=0;
    for(int i=last[x];i;i=e[i].pre)
    if(e[i].too!=fa&&!isrt[e[i].too])
    {
        dfs(e[i].too,x);
        if(mx1[e[i].too]>mx1[x])mx2[x]=mx1[x],mx1[x]=mx1[e[i].too];
        else if(mx1[e[i].too]>mx2[x])mx2[x]=mx1[e[i].too];
    }
    ans=max(ans,mx1[x]+mx2[x]-(d[x]<<1));
}
inline int dfs2(int x,int fa)
{
    if(x==ed)return len++,1;
    for(int i=last[x];i;i=e[i].pre)
    if(e[i].too!=fa)if(dfs2(e[i].too,x))
    return rt[++cnt]=x,isrt[x]=1,len++,1;
    return 0;
}
inline int dis(int x,int y){if(x>=y)return x-y;return len-(y-x);}
inline void work()
{
    int l=1,r=0;
    for(int i=(len>>1);i;q[++r]=i,i--)
    while(l<=r&&mx1[rt[q[r]]]+dis(q[r],cnt)<=mx1[rt[i]]+dis(i,cnt))r--;
    for(int i=cnt;i;i--)
    {
        while(l<=r&&(dis(q[l],i)>(len>>1)||q[l]==i))l++;
        ans=max(ans,mx1[rt[i]]+mx1[rt[q[l]]]+dis(q[l],i));
        while(l<=r&&mx1[rt[q[r]]]+dis(q[r],i)<=mx1[rt[i]])r--;
        q[++r]=i;
    }
}
int main()
{
    freopen("road.in","r",stdin);
    freopen("road.out","w",stdout);
    read(n);read(m);
    for(int i=1;i<n;i++)read(x),read(y),add(x,y),add(y,x);
    for(int i=1;i<=m;i++)
    {
        read(st);read(ed);ans=len=cnt=0;
        memset(isrt,0,sizeof(isrt));d[0]=-1;
        rt[++cnt]=ed;isrt[ed]=1;dfs2(st,0);
        for(int j=1;j<=cnt;j++)dfs(rt[j],0),ans=max(ans,mx1[rt[j]]+(len>>1));
        work();printf("%d\n",ans);
    }
    return 0;
}