POJ 2374 线段树建图+Dijkstra

题意：

思路：
线段树+Dijkstra（要堆优化的）

线段树要支持打标记
一个栅栏 拆成两个点 ：左和右
新加一个栅栏的时候 看看左端点有没有被覆盖过
如果有的话 就分别从覆盖的那条线段的左右向当前的左端点连一条边权为距离的边

右端点同理

跑一遍Dijkstra 就好啦

复杂度：O（nlogn）

//By SiriusRen#include <queue>#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int N=100500;int n,s,xx,tree[N*16],first[N],next[N*4],v[N*4],w[N*4],tot,dis[N],vis[N];struct Fence{int l,r;}fence[N];struct Node{int now,weight;Node(){}Node(int x,int y){now=x,weight=y;}}jy;bool operator < (Node a,Node b){return a.weight>b.weight;}void insert(int l,int r,int pos){    if(l>=fence[xx].l&&r<=fence[xx].r){tree[pos]=xx;return;}    int mid=(l+r)>>1,lson=pos<<1,rson=pos<<1|1;    if(mid<fence[xx].l)insert(mid+1,r,rson);    else if(mid>=fence[xx].r)insert(l,mid,lson);    else insert(l,mid,lson),insert(mid+1,r,rson);}int query(int l,int r,int pos,int x){    if(l==r){return tree[pos];}    int mid=(l+r)>>1,lson=pos<<1,rson=pos<<1|1;    if(tree[pos])tree[lson]=tree[rson]=tree[pos],tree[pos]=0;    if(x<mid)return query(l,mid,lson,x);    else return query(mid+1,r,rson,x);}void add(int x,int y,int z){w[tot]=z,v[tot]=y,next[tot]=first[x],first[x]=tot++;}void deal(){    int tempx=query(-N,N,1,fence[xx].l);    add(tempx<<1,xx<<1,abs(fence[tempx].l-fence[xx].l));    add(tempx<<1|1,xx<<1,abs(fence[tempx].r-fence[xx].l));    int tempy=query(-N,N,1,fence[xx].r);    add(tempy<<1,xx<<1|1,abs(fence[tempy].l-fence[xx].r));    add(tempy<<1|1,xx<<1|1,abs(fence[tempy].r-fence[xx].r));    insert(-N,N,1);}void Dijkstra(){    memset(dis,0x3f,sizeof(dis)),dis[0]=0;    priority_queue<Node>pq;pq.push(jy);    while(!pq.empty()){        Node t=pq.top();pq.pop();        if(vis[t.now])continue;        vis[t.now]=1;        for(int i=first[t.now];~i;i=next[i])            if(!vis[v[i]]&&dis[v[i]]>dis[t.now]+w[i]){                dis[v[i]]=dis[t.now]+w[i];                pq.push(Node(v[i],dis[v[i]]));            }    }}int main(){    scanf("%d%d",&n,&s);    memset(first,-1,sizeof(first)),add(0,1,0);    for(xx=1;xx<=n;xx++)scanf("%d%d",&fence[xx].l,&fence[xx].r),deal();    xx++,fence[xx].l=fence[xx].r=s;deal(),add(xx<<1,xx<<1|1,0);    Dijkstra();    printf("%d\n",dis[xx<<1|1]);}