题目链接：http://bestcoder.hdu.edu.cn/contests/contest_showproblem.php?cid=863&pid=1002
题目：
解题报告：
根据题目给的数据范围，用Floyd算法优化可以过，图可能存在重边，所以要取权值最小的边。
AC代码：
1 #include<bits/stdc++.h> 2 #define numm ch-48 3 #define pd putchar(' ') 4 #define pn putchar(' ') 5 #define pb push_back 6 #define fi first 7 #define se second 8 #define fre1 freopen("1.txt","r",stdin) 9 #define fre2 freopen("3.txt","w",stdout) 10 #define bug cout<<"*******************"<<endl; 11 #define debug(args...) cout<<#args<<"->"<<args<<" "; 12 using namespace std; 13 template <typename T> 14 void read(T &res) { 15 bool flag=false;char ch; 16 while(!isdigit(ch=getchar())) (ch=='-')&&(flag=true); 17 for(res=numm;isdigit(ch=getchar());res=(res<<1)+(res<<3)+numm); 18 flag&&(res=-res); 19 } 20 template <typename T> 21 void write(T x) { 22 if(x<0) putchar('-'),x=-x; 23 if(x>9) write(x/10); 24 putchar(x%10+'0'); 25 } 26 typedef long long ll; 27 typedef unsigned long long ull; 28 const int maxn=1010; 29 const int maxm=505; 30 const int mod=1e9+7; 31 const int inv2=500000004; 32 const int inf=0x3f3f3f3f; 33 const ll INF=0x3f3f3f3f3f3f3f3f; 34 //const int N=32; 35 ll A[maxn][maxn]; 36 ll a[maxn][maxn]; 37 int N; 38 void Floyd_1(){ 39 for(int k = 1; k <= N; k++){ 40 for(int i = 1; i <= N; i++){ 41 ll t = A[i][k]; 42 if(t!=INF) 43 for(int j = 1; j <= i; j++) { 44 if(t+A[k][j]<A[i][j]) { 45 A[i][j]=t+A[k][j]; 46 A[j][i]=A[i][j]; 47 a[i][j]=max(a[i][j],(ll)k); 48 a[j][i]=max(a[j][i],(ll)k); 49 } 50 } 51 } 52 } 53 return ; 54 } 55 int main() 56 { 57 // #define local 58 #ifdef local 59 fre1; 60 fre2; 61 #endif // local 62 int _,m; 63 read(_); 64 while(_--) { 65 read(N),read(m); 66 for(int i=1;i<=N;i++) { 67 for(int j=1;j<=N;j++) 68 A[i][j]=(i==j?0:INF),a[i][j]=0; 69 } 70 for(int i=1;i<=m;i++) { 71 int u,v; 72 ll w; 73 read(u);read(v);read(w); 74 A[u][v]=min(w,A[u][v]); 75 A[v][u]=min(w,A[v][u]); 76 } 77 Floyd_1(); 78 ll ans=0; 79 const ll mod=998244353; 80 for(int i=1;i<=N;i++) 81 for(int j=1;j<=N;j++) 82 ans=(ans+a[i][j])%mod; 83 write(ans);pn; 84 } 85 return 0; 86 }