BZOJ5254 FJWC2018红绿灯(线段树)

  注意到一旦在某个路口被红灯逼停,剩下要走的时间是固定的。容易想到预处理出在每个路口被逼停后到达终点的最短时间,这样对于每个询问求出其最早在哪个路口停下就可以了。对于预处理,从下一个要停的路口倒推即可。问题只剩下如何求出下一个要停的路口,这相当于求满足di,j%(g+r)>=g的最小j,对d做一个前缀和,那么显然满足条件的是一个值域区间,线段树维护值域区间的路口最小编号即可。对于询问要处理的也与此类似。注意家里没有红灯。(?)

#include<iostream> 
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
using namespace std;
#define ll long long
#define N 50010
char getc(){char c=getchar();while ((c<'A'||c>'Z')&&(c<'a'||c>'z')&&(c<'0'||c>'9')) c=getchar();return c;}
int gcd(int n,int m){return m==0?n:gcd(m,n%m);}
int read()
{
    int x=0,f=1;char c=getchar();
    while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}
    while (c>='0'&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();
    return x*f;
}
int n,m,g,r,a[N],root,cnt;
ll d[N],s[N];
struct data{int l,r,x;
}tree[N<<5];
void ins(int &k,int l,int r,int p,int i)
{
    if (!k) k=++cnt,tree[k].x=n+1;
    tree[k].x=min(tree[k].x,i);
    if (l==r) return;
    int mid=l+r>>1;
    if (p<=mid) ins(tree[k].l,l,mid,p,i);
    else ins(tree[k].r,mid+1,r,p,i);
}
int query(int k,int l,int r,int x,int y)
{
    if (!k) return n+1;
    if (l==x&&r==y) return tree[k].x;
    int mid=l+r>>1;
    if (y<=mid) return query(tree[k].l,l,mid,x,y);
    else if (x>mid) return query(tree[k].r,mid+1,r,x,y);
    else return min(query(tree[k].l,l,mid,x,mid),query(tree[k].r,mid+1,r,mid+1,y));
}
int getnxt(ll x)
{
    x%=g+r;if (x<0) x+=g+r;
    if (x<=g) return query(root,0,g+r-1,g-x,g+r-1-x);
    else return min(query(root,0,g+r-1,0,g+r-1-x),query(root,0,g+r-1,g+r-(x-g),g+r-1));
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen("bzoj5254.in","r",stdin);
    freopen("bzoj5254.out","w",stdout);
    const char LL[]="%I64d
";
#else
    const char LL[]="%lld
";
#endif
    n=read(),g=read(),r=read();
    for (int i=0;i<=n;i++) s[i+1]=s[i]+(a[i]=read());
    for (int i=n;i>=0;i--)
    {
        int nxt=getnxt(-s[i]);
        if (nxt==n+1) d[i]=s[n+1]-s[i];
        else d[i]=d[nxt]+((s[nxt]-s[i])/(g+r)+1)*(g+r);
        if (i) ins(root,0,g+r-1,s[i]%(g+r),i);
    }
    m=read();
    while (m--)
    {
        int x=read();
        int nxt=getnxt(x);
        if (nxt==n+1) printf(LL,x+s[n+1]);
        else printf(LL,d[nxt]+((s[nxt]+x)/(g+r)+1)*(g+r));
    }
    return 0;
}
原文地址:https://www.cnblogs.com/Gloid/p/10095760.html