多源最短路算法——floyd算法

 1 #include
 2 #define ll long long 
 3 #define scan(i) scanf("%d",&i)
 4 #define scand(i) scanf("%lf",&i)
 5 #define scanl(i) scanf("%lld",&i)
 6 #define f(i,a,b) for(int i=a;i<=b;i++) 
 7 #define pb(i) push_back(i)
 8 #define ppb pop_back()
 9 #define pf printf
10 #define dbg(args...) cout<<#args<<" : "<11 using namespace std;
12 int t,n,m; 
13 int dis[302][302];
14 int x,y,w;
15 void floyd(){
16     f(k,0,n-1){
17         f(i,0,n-1){
18             f(j,0,n-1){
19                 if(i==j) dis[i][j]=0;
20                 else dis[i][j]=min(dis[i][j],dis[i][k]+dis[k][j]);
21             }
22         }
23     }
24 }
25 int main(){
26     scan(t);
27     f(kk,1,t){
28         scanf("%d%d",&n,&m);
29         memset(dis,0x3f,sizeof(dis));
30         f(i,1,m){
31             scanf("%d%d%d",&x,&y,&w);
32             dis[x][y]=w;
33         }
34         floyd();
35         f(i,1,6){
36             scanf("%d%d",&x,&y);
37             pf("%d\n",-dis[y][x]);
38             dis[x][y]=-dis[y][x];
39             if(i-6) floyd();
40         }
41         //pf("Case #%d: %lld,kk,ans);
42     }
43     return 0;
44 } 

算法复杂度O(n^2)。