【bzoj3387-跨栏训练】线段树+dp

  1 #include<cstdio>
  2 #include<cstdlib>
  3 #include<cstring>
  4 #include<iostream>
  5 #include<ctime>
  6 #include<queue>
  7 #include<algorithm>
  8 using namespace std;
  9 
 10 const int N=2*2*50010,INF=(int)1e9;
 11 int n,st,pl,tl,r[N],f[N][2];
 12 struct node{
 13     int d,id,tmp;
 14 }p[N];
 15 struct nd{
 16     int x1,x2;
 17 }a[N];
 18 struct trnode{
 19     int l,r,lc,rc,id,lazy;
 20 }t[2*N];
 21 
 22 bool cmp_d(node x,node y){return x.d<y.d;}
 23 int myabs(int x){return x>0 ? x:-x;}
 24 int minn(int x,int y){return x<y ? x:y;}
 25 int maxx(int x,int y){return x>y ? x:y;}
 26 
 27 int bt(int l,int r)
 28 {
 29     int x=++tl;
 30     t[x].l=l;t[x].r=r;
 31     t[x].lc=t[x].rc=0;
 32     t[x].id=INF;t[x].lazy=INF;
 33     if(l<r)
 34     {
 35         int mid=(l+r)/2;
 36         t[x].lc=bt(l,mid);
 37         t[x].rc=bt(mid+1,r);
 38     }
 39     return x;
 40 }
 41 
 42 void upd(int x)
 43 {
 44     if(t[x].lazy==INF) return ;
 45     int id=t[x].lazy,lc=t[x].lc,rc=t[x].rc;
 46     t[x].lazy=INF;
 47     t[x].id=minn(t[x].id,id);
 48     if(lc) t[lc].lazy=minn(t[lc].lazy,id);
 49     if(rc) t[rc].lazy=minn(t[rc].lazy,id);
 50 }
 51 
 52 void change(int x,int l,int r,int id)
 53 {
 54     upd(x);
 55     if(t[x].l==l && t[x].r==r) 
 56     {
 57         t[x].lazy=minn(t[x].lazy,id);
 58         upd(x);
 59         return ;
 60     }
 61     int lc=t[x].lc,rc=t[x].rc,mid=(t[x].l+t[x].r)/2;
 62     if(r<=mid) change(lc,l,r,id);
 63     else if(l>mid) change(rc,l,r,id);
 64     else
 65     {
 66         change(lc,l,mid,id);
 67         change(rc,mid+1,r,id);
 68     }
 69 }
 70 
 71 int query(int x,int p)
 72 {
 73     upd(x);
 74     if(t[x].l==t[x].r) return t[x].id;
 75     int lc=t[x].lc,rc=t[x].rc,mid=(t[x].l+t[x].r)/2;
 76     if(p<=mid) return query(lc,p);
 77     else return query(rc,p);
 78 }
 79 
 80 int main()
 81 {
 82     // freopen("a.in","r",stdin);
 83     // freopen("me.out","w",stdout);
 84     freopen("obstacle.in","r",stdin);
 85     freopen("obstacle.out","w",stdout);
 86     scanf("%d%d",&n,&st);
 87     int x,ed;ed=0;pl=0;tl=0;
 88     p[++pl].d=st;p[pl].id=n+1;
 89     p[++pl].d=ed;p[pl].id=n+2;
 90     for(int i=1;i<=n;i++)
 91     {
 92         scanf("%d%d",&a[i].x1,&a[i].x2);
 93         if(a[i].x1>a[i].x2) swap(a[i].x1,a[i].x2);
 94         p[++pl].d=a[i].x1;p[pl].id=i;p[pl].tmp=0;
 95         p[++pl].d=a[i].x2;p[pl].id=i;p[pl].tmp=1;
 96     }
 97     sort(p+1,p+1+pl,cmp_d);
 98     int mx=0;p[0].d=INF;
 99     for(int i=1;i<=pl;i++)
100     {
101         if(p[i].d!=p[i-1].d) mx++,r[mx]=p[i].d;
102         if(p[i].id==n+1) st=mx;
103         else if(p[i].id==n+2) ed=mx;
104         else
105         {
106             if(p[i].tmp==0) a[p[i].id].x1=mx;
107             else a[p[i].id].x2=mx;
108         }
109     }
110     bt(1,mx);
111     change(1,st,st,n+1);
112     a[n+1].x1=a[n+1].x2=st;
113     f[n+1][0]=f[n+1][1]=0;
114     a[0].x1=a[0].x2=ed;
115     for(int i=n;i>=0;i--)
116     {
117         x=query(1,a[i].x1);
118         if(x<INF) f[i][0]=minn(f[x][0]+myabs(r[a[x].x1]-r[a[i].x1]),f[x][1]+myabs(r[a[x].x2]-r[a[i].x1]));
119         else f[i][0]=myabs(r[st]-r[a[i].x1]);
120         x=query(1,a[i].x2);
121         if(x<INF) f[i][1]=minn(f[x][0]+myabs(r[a[x].x1]-r[a[i].x2]),f[x][1]+myabs(r[a[x].x2]-r[a[i].x2]));
122         else f[i][1]=myabs(r[st]-r[a[i].x2]);
123         change(1,a[i].x1,a[i].x2,i);
124     }
125     printf("%d\n",f[0][0]);
126     return 0;
127 }