zoukankan      html  css  js  c++  java
  • 洛谷 1951 收费站

    【题解】

      二分+dijkstra

      二分需要交的过路费,然后跑dijkstra判断最短路是否小于s

     1 #include<cstdio>
     2 #include<cstring>
     3 #include<algorithm>
     4 #define LL long long
     5 #define rg register
     6 #define N 10010
     7 using namespace std;
     8 int n,m,st,ed,s,tot,fa,son,last[N],pos[N],f[N],b[N];
     9 LL dis[N];
    10 struct edge{int to,pre,w;}e[100010];
    11 struct rec{int u,v,w;}r[50010];
    12 struct heap{int p;LL d;}h[N];
    13 inline int read(){
    14     int k=0,f=1; char c=getchar();
    15     while(c<'0'||c>'9')c=='-'&&(f=-1),c=getchar();
    16     while('0'<=c&&c<='9')k=k*10+c-'0',c=getchar();
    17     return k*f;
    18 }
    19 inline void up(int x){
    20     while((fa=x>>1)&&h[fa].d>h[x].d) swap(h[fa],h[x]),swap(pos[h[fa].p],pos[h[x].p]),x=fa;
    21 }
    22 inline void down(int x){
    23     while((son=x<<1)<=tot){
    24         if(h[son].d>h[son+1].d&&son<tot) son++;
    25         if(h[son].d<h[x].d) swap(h[son],h[x]),swap(pos[h[son].p],pos[h[x].p]),x=son;
    26         else return;
    27     }
    28 }
    29 inline void dijkstra(int x){
    30     for(rg int i=1;i<=n;i++) dis[i]=1e17;
    31     h[pos[x]=tot=1]=(heap){x,dis[x]=0};
    32     while(tot){
    33         int now=h[1].p; pos[h[tot].p]=1; h[1]=h[tot--]; if(tot) down(1);
    34         for(rg int i=last[now],to;i;i=e[i].pre)if(dis[to=e[i].to]>dis[now]+e[i].w){
    35             dis[to]=dis[now]+e[i].w;
    36             if(!pos[to]) h[pos[to]=++tot]=(heap){to,dis[to]};
    37             else h[pos[to]].d=dis[to];
    38             up(pos[to]);
    39         }
    40     }
    41 }
    42 inline bool check(int x){
    43     memset(last,0,sizeof(last));
    44     memset(pos,0,sizeof(pos));
    45     tot=0;
    46     for(rg int i=1;i<=m;i++){
    47         int u=r[i].u,v=r[i].v,w=r[i].w;
    48         if(f[u]<=x&&f[v]<=x){
    49             e[++tot]=(edge){u,last[v],w}; last[v]=tot;
    50             e[++tot]=(edge){v,last[u],w}; last[u]=tot;
    51         }
    52     }
    53     dijkstra(st);
    54     if(dis[ed]<=s) return 1;
    55     return 0;
    56 }
    57 int main(){
    58     n=read(); m=read(); st=read(); ed=read(); s=read();
    59     for(rg int i=1;i<=n;i++) f[i]=b[i]=read();
    60     sort(b+1,b+1+n);
    61     for(rg int i=1;i<=m;i++) r[i].u=read(),r[i].v=read(),r[i].w=read();
    62     int l=0,r=n+1;
    63     while(l+1<r){
    64         int mid=(l+r)>>1;
    65         if(check(b[mid])) r=mid; else l=mid;
    66     }
    67     printf("%d
    ",(r==n+1)?-1:b[r]);
    68     return 0;
    69 }
  • 相关阅读:
    ubuntu下安装VMware tools
    ubuntu 输入su提示认证失败的解决方法
    Squishy Bird 压扁小鸟
    js 毫秒转日期(yy-MM-dd hh:mm:ss)
    js--使用构造器函数来新建对象及操作
    css中table样式
    js 字符串截取
    JavaScript中Math--random()/floor()/round()/ceil()
    canvas draw a image
    html5 canvas simple drawing
  • 原文地址:https://www.cnblogs.com/DriverLao/p/9863178.html
Copyright © 2011-2022 走看看