BOJ 1452

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k元环问题，即邻接矩阵的k次幂

用矩阵快速幂加速

#include <cstdio>#include <cstring>#include <algorithm>#define N 110#define inf -1000000000using namespace std;int n,m;struct Matrix{int d[N][N];};Matrix multiply(Matrix a,Matrix b){Matrix res;int i,j,k;for(i=1;i<=n;i++)for(j=1;j<=n;j++){res.d[i][j]=inf;for(k=1;k<=n;k++){if(a.d[i][k] != inf && b.d[k][j] != inf)res.d[i][j]=max(res.d[i][j],a.d[i][k]+b.d[k][j]);}}return res;}Matrix solve(Matrix mp,int k){int i,j;Matrix res;for(i=1;i<=n;i++)for(j=1;j<=n;j++)if(i==j) res.d[i][j]=0;else res.d[i][j]=inf;while(k){if(k%2){res=multiply(res,mp);}mp=multiply(mp,mp);k>>=1;}return res;}int main(){int i,j,k,t,T;int u,v,w;Matrix mp;scanf("%d",&T);for(t=1;t<=T;t++){scanf("%d %d %d",&n,&m,&k);for(i=1;i<=n;i++)              //之前一直WA是这个初始化写在scanf之前了....for(j=1;j<=n;j++)mp.d[i][j]=inf;for(i=1;i<=m;i++){scanf("%d %d %d",&u,&v,&w);mp.d[u][v]=max(mp.d[u][v],w);}mp=solve(mp,k);int ans=inf;for(i=1;i<=n;i++) ans=max(ans,mp.d[i][i]);if(ans==inf) printf("No solution\n");else printf("%d\n",ans);}return 0;}