bzoj2763 飞行路线 二维SPFA

Posted 2020-10-02 Loser Of Life

填坑填坑填坑……链接：http://www.lydsy.com/JudgeOnline/problem.php?id=2763

题意：有$m$次免费机会，求出最小值。

二维最短路没什么说的。注意时间很坑人，要用双端队列优化$SPFA$（我再说一遍堆优化SPFA是不存在的……）

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 using namespace std;
 6 const int maxm=50005,maxt=15,maxn=10005;
 7 struct pii
 8 {
 9     int pos,tim;
10     bool operator <(const pii &b)const 
11     {
12         return pos>b.pos;
13     }
14 };
15 #include<deque>
16 deque<pii>heap;
17 int dis[maxn][maxt],n,m,k,s,t;
18 bool inqueue[maxn][maxt];
19 struct node
20 {
21     int from,to,dis,next;
22 }edge[maxm<<1];
23 int head[maxn],tot;
24 void addedge(int u,int v,int w)
25 {
26     edge[++tot]=(node){u,v,w,head[u]};head[u]=tot;
27 }
28 void Push(pii a)
29 {
30     if(a<heap.front())heap.push_front(a);
31     else heap.push_back(a);
32 }
33 void spfa()
34 {
35     dis[s][k]=0;Push((pii){s,k});
36     inqueue[s][k]=1;
37     while(!heap.empty())
38     {
39         pii s=heap.front();heap.pop_front();
40         int pos=s.pos,tim=s.tim,dist=dis[pos][tim];inqueue[pos][tim]=0;
41         for(int i=head[pos];i;i=edge[i].next)
42         {
43             int v=edge[i].to;
44             if(dis[v][tim]>dist+edge[i].dis)
45             {
46                 dis[v][tim]=dist+edge[i].dis;
47                 if(!inqueue[v][tim])Push((pii){v,tim}),inqueue[v][tim]=1;
48             }
49             if(tim&&dis[v][tim-1]>dist)
50             {
51                 dis[v][tim-1]=dist;
52                 if(!inqueue[v][tim-1])Push((pii){v,tim-1}),inqueue[v][tim-1]=1;
53             }
54         }
55     }
56 }
57 int haha()
58 {
59     scanf("%d%d%d",&n,&m,&k);scanf("%d%d",&s,&t);
60     for(int i=1;i<=m;i++)
61     {
62         int x,y,z;scanf("%d%d%d",&x,&y,&z);
63         addedge(x,y,z);addedge(y,x,z);
64     }
65     memset(dis,0x3f,sizeof(dis));
66     spfa();
67     int ans=0x7fffffff;
68     for(int i=0;i<=k;i++)ans=min(ans,dis[t][i]);
69     printf("%d\n",ans);
70 }
71 int sb=haha();
72 int main(){;}

bzoj2763