这题确实水，纯板子，考试意外出错，只拿了暴力分QAQ
tarjan缩点加上拓扑排序，注意这里求最短路径时不能用最小生成树
因为是单向边，不然就可能不是一个联通图了....
1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<string> 5 #include<cmath> 6 #include<queue> 7 #include<stack> 8 #include<vector> 9 #include<algorithm> 10 #define MAXN 100001 11 #define pt printf("----------- "); 12 #define push_back ps 13 #define ll long long 14 using namespace std; 15 int read() 16 { 17 int x=0;char c=getchar(); 18 while(c<'0'||c>'9')c=getchar(); 19 while(c<='9'&&c>='0'){x=x*10+c-'0';c=getchar();} 20 return x; 21 } 22 struct node{int to,n,w;}e1[MAXN],e2[MAXN];int head1[MAXN],tot1,head2[MAXN],tot2; 23 void add1(int u,int v,int w){e1[++tot1].to=v;e1[tot1].w=w;e1[tot1].n=head1[u];head1[u]=tot1;} 24 void add2(int u,int v,int w){e2[++tot2].to=v;e2[tot2].w=w;e2[tot2].n=head2[u];head2[u]=tot2;} 25 int low[MAXN],dfn[MAXN]; 26 stack<int>q; 27 bool vis[MAXN]; 28 int de,cnt=0; 29 int root=1; 30 int n,m; 31 int belong[MAXN];int ru[MAXN]; 32 void tarjan(int x) 33 { 34 low[x]=dfn[x]=++de; 35 vis[x]=1;q.push(x); 36 int js=0; 37 for(int i=head1[x];i;i=e1[i].n) 38 { 39 int to=e1[i].to; 40 if(!dfn[to]) 41 { 42 tarjan(to); 43 low[x]=min(low[x],low[to]); 44 } 45 else if(vis[to]) 46 { 47 low[x]=min(low[x],low[to]); 48 } 49 } 50 if(dfn[x]==low[x]) 51 { 52 cnt++; 53 int top=0; 54 do 55 { 56 top=q.top();vis[top]=0;q.pop();belong[top]=cnt; 57 // printf("top=%d cnt=%d ",top,cnt); 58 } 59 while(top!=x); 60 } 61 } 62 void init() 63 { 64 for(int x=1;x<=n;++x) 65 { 66 for(int i=head1[x];i;i=e1[i].n) 67 { 68 int to=e1[i].to; 69 if(belong[x]==belong[to])continue; 70 add2(belong[x],belong[to],e1[i].w); 71 ru[belong[to]]++; 72 //chu[belong[x]]++; 73 // printf("belong[%d]=%d-----belong[%d]=%d ",x,belong[x],to,belong[to]); 74 } 75 } 76 /* for(int i=1;i<=n;++i) 77 { 78 79 }*/ 80 } 81 queue<int>qq;int f[MAXN]; 82 int biao[MAXN]; 83 int ans=0; 84 void tuopu(int top) 85 { 86 memset(f,0x3f3f3f,sizeof(f)); 87 qq.push(top); 88 f[top]=0; 89 while(!qq.empty()) 90 { 91 int x=qq.front();qq.pop(); 92 for(int i=head2[x];i;i=e2[i].n) 93 { 94 int to=e2[i].to; 95 ru[to]--; 96 f[to]=min(f[to],e2[i].w); 97 if(ru[to]==0) 98 { 99 qq.push(to); 100 ans+=f[to]; 101 } 102 } 103 } 104 } 105 void work() 106 { 107 if(m==n-1) 108 { 109 for(int i=1;i<=m;++i) 110 { 111 int x,y,w; 112 scanf("%d%d%d",&x,&y,&w); 113 ans+=w; 114 } 115 printf("%d ",ans); 116 } 117 else 118 { 119 for(int i=1;i<=m;++i) 120 { 121 int x,y,w; 122 scanf("%d%d%d",&x,&y,&w); 123 x++;y++; 124 //printf("x=%d y=%d ",x,y); 125 add1(x,y,w); 126 } 127 tarjan(root); 128 init(); 129 tuopu(belong[root]); 130 printf("%d ",ans); 131 } 132 } 133 int main() 134 { 135 while(cin>>n>>m) 136 { 137 if(n==0&&m==0)break; 138 memset(low,0,sizeof(low));memset(dfn,0,sizeof(dfn)); 139 memset(belong,0,sizeof(belong));memset(ru,0,sizeof(ru)); 140 memset(biao,0,sizeof(biao)); 141 ans=0;cnt=0;de=0;tot1=0;tot2=0;memset(head1,0,sizeof(head1));memset(head2,0,sizeof(head2)); 142 work(); 143 } 144 }