输入一个无向图<V,E> V<=1e5, E<=3e5
现在另外给k条边(u=1,v=s[k],w=y[k])
问在不影响从结点1出发到所有结点的最短路的前提下，最多可以删除k条边的多少条
跑最短路的时候维护或者统计就好了
一开始用spfa.然后TLE 45...好久没写 Dij+堆优化 ...
p.s.优先队列默认大顶堆
Dij+堆优化 264ms
1 #include <cstdio> 2 #include <cstring> 3 #include <iostream> 4 #include <algorithm> 5 #include <cmath> 6 #include <queue> 7 #include <set> 8 #include <string> 9 using namespace std; 10 11 #define ll long long 12 #define maxn 100010 13 #define maxm 700010 14 15 int head[maxn]; 16 struct edge{ 17 int v,w,nxt; 18 }e[maxm]; 19 int E; 20 void init(){E=0;memset(head,-1,sizeof(head));} 21 void addedge(int u,int v,int w){ 22 e[E].v=v,e[E].w=w,e[E].nxt=head[u]; 23 head[u]=E++; 24 } 25 priority_queue<pair<ll,int> >que; 26 bool vis[maxn]; 27 //ll d[maxn]; 28 int main(){ 29 int n,m,k; 30 while(~scanf("%d%d%d",&n,&m,&k)){ 31 init(); 32 for(int i=0;i<m;++i){ 33 int u,v,w; 34 scanf("%d%d%d",&u,&v,&w); 35 addedge(u,v,w); 36 addedge(v,u,w); 37 } 38 que.push(make_pair(0ll,1)); 39 for(int i=0;i<k;++i){ 40 int s,y; 41 scanf("%d%d",&s,&y); 42 que.push(make_pair(0ll-y,-s)); 43 } 44 memset(vis,false,sizeof(vis)); 45 int ans=0; 46 while(!que.empty()){ 47 pair<ll,int> tmp = que.top();que.pop(); 48 ll dis = -tmp.first; 49 int u = tmp.second; 50 if(u<0){ 51 u=-u; 52 if(vis[u])++ans; 53 } 54 if(vis[u]) continue; 55 vis[u]=true; 56 //d[u] = dis; 57 for(int i=head[u];i!=-1;i=e[i].nxt) 58 if(vis[e[i].v]==false) 59 que.push(make_pair( -dis-e[i].w, e[i].v)); 60 } 61 printf("%d ",ans); 62 } 63 return 0; 64 }
spfa TLE 45
1 #include <cstdio> 2 #include <cstring> 3 #include <iostream> 4 #include <algorithm> 5 #include <cmath> 6 #include <queue> 7 #include <set> 8 #include <string> 9 using namespace std; 10 11 #define ll long long 12 #define maxn 100010 13 #define maxm 700010 14 15 int head[maxn]; 16 struct edge{ 17 int v,w,nxt; 18 int k; 19 }e[maxm]; 20 int E; 21 void init(){E=0;memset(head,-1,sizeof(head));} 22 void addedge(int u,int v,int w,int kind){ 23 e[E].v=v,e[E].w=w,e[E].nxt=head[u]; 24 e[E].k = kind; 25 head[u]=E++; 26 } 27 int q[maxn]; 28 bool inq[maxn]; 29 bool bus[maxn]; 30 ll dis[maxn]; 31 void spfa(){ 32 int hd=0,tl=0; 33 q[tl++]=1; 34 memset(dis,0x3f,sizeof(dis)); 35 dis[1]=0; 36 memset(inq,false,sizeof(inq)); 37 inq[1]=true; 38 memset(bus,false,sizeof(bus)); 39 while(hd!=tl){ 40 int u = q[hd++]; 41 if(hd==maxn)hd=0; 42 inq[u] = false; 43 for(int i=head[u];i!=-1;i=e[i].nxt){ 44 int v = e[i].v, w = e[i].w, k = e[i].k; 45 if(dis[u]+w < dis[v]){ 46 dis[v] = dis[u]+w; 47 bus[v] = false; 48 if(k==0) bus[v]=true; 49 if(inq[v]==false){ 50 inq[v]=true; 51 q[tl++]=v; 52 if(tl==maxn)tl=0; 53 } 54 }else if(dis[u]+w == dis[v]){ 55 if(k==0) bus[v]=true; 56 } 57 } 58 } 59 } 60 int si[100010],yi[100010]; 61 int main(){ 62 int n,m,k; 63 while(~scanf("%d%d%d",&n,&m,&k)){ 64 init(); 65 for(int i=0;i<m;++i){ 66 int u,v,w; 67 scanf("%d%d%d",&u,&v,&w); 68 addedge(u,v,w,0); 69 addedge(v,u,w,0); 70 } 71 for(int i=0;i<k;++i){ 72 scanf("%d%d",si+i,yi+i); 73 addedge(1,si[i],yi[i],1); 74 } 75 spfa(); 76 int ans=0; 77 for(int i=0;i<k;++i){ 78 int v = si[i]; 79 if(dis[v] < yi[i]) ++ans; 80 else { 81 if(bus[v]==false)bus[v]=true; 82 else ++ans; 83 } 84 } 85 printf("%d ",ans); 86 } 87 return 0; 88 }