mirror of
https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
89 lines
2.1 KiB
C++
89 lines
2.1 KiB
C++
#include<iostream>
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#include<cstdio>
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#include<queue>
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#include<vector>
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using namespace std;
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const int MAXN=1000+10;
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const int inf=1<<30;
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struct Node{
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int v,w,id;
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};
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vector<Node>vet[MAXN];
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int path[MAXN];
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int dist[MAXN];
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bool visited[MAXN];
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bool mark[MAXN*50];
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int id[MAXN];
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int n,m;
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bool tag;
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void SPFA(int u){
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for(int i=1;i<=n;i++)dist[i]=inf;
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dist[u]=0;
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memset(visited,false,sizeof(visited));
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queue<int>Q;
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Q.push(u);
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while(!Q.empty()){
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int u=Q.front();
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Q.pop();
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visited[u]=false;
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for(int i=0;i<vet[u].size();i++){
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int v=vet[u][i].v;
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int w=vet[u][i].w;
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int ID=vet[u][i].id;
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if(mark[vet[u][i].id])continue;
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if(dist[u]+w<dist[v]){
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dist[v]=dist[u]+w;
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if(tag)path[v]=u,id[v]=ID;
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if(!visited[v]){
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Q.push(v);
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visited[v]=true;
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}
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}
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}
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}
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}
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int main(){
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int _case;
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scanf("%d",&_case);
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while(_case--){
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scanf("%d%d",&n,&m);
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for(int i=1;i<=n;i++)vet[i].clear();
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memset(path,-1,sizeof(path));
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memset(mark,false,sizeof(mark));
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for(int i=1;i<=m;i++){
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int u,v,w;
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scanf("%d%d%d",&u,&v,&w);
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Node p1,p2;
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p1.v=u,p2.v=v;
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p1.w=p2.w=w;
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p1.id=p2.id=i;
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vet[u].push_back(p2);
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vet[v].push_back(p1);
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}
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tag=true;
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SPFA(1);
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tag=false;
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if(dist[n]==inf){
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printf("-1\n");
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continue;
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}
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int ans=0;
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bool flag=true;
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for(int u=n;u!=-1;u=path[u]){
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mark[id[u]]=true;
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SPFA(1);
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mark[id[u]]=false;
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if(dist[n]==inf){
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printf("-1\n");
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flag=false;
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break;
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}
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ans=max(ans,dist[n]);
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}
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if(flag){
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printf("%d\n",ans);
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}
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}
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return 0;
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}
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