854. Floyd求最短路

Posted 2021-05-14 幽殇默

https://www.acwing.com/problem/content/856/

#include<cstdio>
#include<iostream>
#include<algorithm>
using namespace std;
const int N=210;
const int INF=1e9;
int n,m,k;
int dist[N][N];
void floyd()
{
	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 main(void)
{
	cin>>n>>m>>k;
	for(int i=1;i<=n;i++)
		for(int j=1;j<=n;j++)
			if(i==j) dist[i][j]=0;  //自环
			else dist[i][j]=INF;   
	while(m--)
	{
		int a,b,c; cin>>a>>b>>c;
		dist[a][b]=min(dist[a][b],c);  //存较小的边
	}
	floyd();
	while(k--)
	{
		int a,b; cin>>a>>b;
		if(dist[a][b]>1e9/2) cout<<"impossible"<<endl;
		else cout<<dist[a][b]<<endl;
	}
	return 0;
}