1128. 信使最短路

Posted 2021-10-30 幽殇默

https://www.acwing.com/problem/content/description/1130/

#include<bits/stdc++.h>
using namespace std;
const int N=1e3+10;
int n,m;
int g[N][N],dist[N],st[N];
void Dijkstra()
{
    memset(dist,0x3f,sizeof dist);
    dist[1]=0;
    for(int i=0;i<n;i++)
    {
        int t=-1;
        for(int j=1;j<=n;j++) if(!st[j]&&(t==-1 || dist[j]<dist[t] )) t=j;
        st[t]=1;
        for(int j=1;j<=n;j++) dist[j]=min(dist[j],dist[t]+g[t][j]);
    }
}
int main(void)
{
    memset(g,0x3f,sizeof g);
    cin>>n>>m;
    while(m--)
    {
        int a,b,c; cin>>a>>b>>c;
        g[a][b]=g[b][a]=min(g[a][b],c);
    }
    Dijkstra();
    int ans=0,flag=0;
    for(int i=1;i<=n;i++) 
        if(dist[i]!=0x3f3f3f3f) ans=max(ans,dist[i]);
        else flag=1;
    if(!flag) cout<<ans<<endl;
    else puts("-1");
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
const int N=1e3+10;
int dist[N][N],n,m;
int main(void)
{
    memset(dist,0x3f,sizeof dist);
    cin>>n>>m;
    for(int i=1;i<=n;i++) dist[i][i]=0;
    for(int i=1;i<=m;i++)
    {
        int a,b,c; cin>>a>>b>>c;
        dist[a][b]=dist[b][a]=min(dist[b][a],c);
    }
    for(int k=1;k<=n;k++)
        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++)
                dist[i][j]=min(dist[i][j],dist[i][k]+dist[k][j]);
    int ans=0;
    for(int i=1;i<=n;i++)  ans=max(ans,dist[1][i]);
    if(ans==0x3f3f3f3f) puts("-1");
    else cout<<ans;
    return 0;
}