#include<queue> #include<cstdio> #include<cstring> #include<algorithm> using namespace std; const int maxn=50005; const int maxm=200005; struct node{int id;long long d;}; bool operator <(node a,node b){return a.d>b.d;} int info[maxn],nx[maxm<<1],v[maxm<<1],w[maxm<<1],re[maxm<<1];long long d[5][maxn]; int n,m,en,ans,ecnt,p[5],dp[maxn],vis[maxn],inp[maxn],top[maxn],lef[maxm<<1];priority_queue<node>q; void add(int u1,int v1,int w1,int r){nx[++ecnt]=info[u1];info[u1]=ecnt;v[ecnt]=v1;w[ecnt]=w1;re[ecnt]=r;} void SPFA(int k) { memset(vis,0,sizeof vis); d[k][p[k]]=0;q.push((node){p[k],0}); while(!q.empty()) { node nw=q.top();q.pop(); if(vis[nw.id]==1)continue;vis[nw.id]=1;d[k][nw.id]=nw.d; for(int i=info[nw.id];i;i=nx[i]) if(!((k%2)^re[i])&&d[k][v[i]]>nw.d+w[i])q.push((node){v[i],nw.d+w[i]}); } } int main() { scanf("%d%d",&n,&m);memset(d,0x7f,sizeof d); for(int i=1,u1,v1,w1;i<=m;i++)scanf("%d%d%d",&u1,&v1,&w1),add(u1,v1,w1,1),add(v1,u1,w1,0); for(int k=1;k<=4;k++)scanf("%d",&p[k]),SPFA(k); if(d[1][p[2]]==d[0][0]||d[3][p[4]]==d[0][0]){puts("-1");return 0;} for(int x=1;x<=n;x++) { for(int e=info[x];e;e=nx[e]) if(re[e]&&d[1][x]+w[e]+d[2][v[e]]==d[1][p[2]]&&d[3][x]+w[e]+d[4][v[e]]==d[3][p[4]]) lef[e]=1,inp[v[e]]++; } for(int x=1;x<=n;x++)if(inp[x]==0)top[++en]=x,dp[x]=1; for(int i=1;i<=en;i++) { int nw=top[i]; for(int e=info[nw];e;e=nx[e]) if(lef[e]) { dp[v[e]]=max(dp[v[e]],dp[nw]+1); ans=max(ans,dp[v[e]]);inp[v[e]]--; if(!inp[v[e]])top[++en]=v[e]; } } printf("%d\n",ans); } 来源：博客园
作者：夜伤魄
链接：https://www.cnblogs.com/firecrazy/p/11656407.html