codeforces 864F Cities Excursions

 1 #include <bits/stdc++.h>
 2 #define il inline
 3 #define RG register
 4 #define ll long long
 5 #define M (400005)
 6 #define N (3005)
 7 
 8 using namespace std;
 9 
10 struct data{ int i,u,v,k; }q[M];
11 
12 int ans[M],dfn[N],low[N],st[N],inst[N],Q,n,m,cnt,top;
13 
14 vector<int> g[N],c[N];
15 
16 il int gi(){
17   RG int x=0,q=1; RG char ch=getchar();
18   while ((ch<‘0‘ || ch>‘9‘) && ch!=‘-‘) ch=getchar();
19   if (ch==‘-‘) q=-1,ch=getchar();
20   while (ch>=‘0‘ && ch<=‘9‘) x=x*10+ch-48,ch=getchar();
21   return q*x;
22 }
23 
24 il int cmp(const data &a,const data &b){ return a.u<b.u; }
25 
26 il void dfs(RG int x,RG int fg){
27   dfn[x]=++cnt,low[x]=1<<30,inst[x]=1,st[++top]=x;
28   if (fg){
29     for (RG int i=0,sz=c[x].size();i<sz;++i)
30       if (q[c[x][i]].k<=top) ans[q[c[x][i]].i]=st[q[c[x][i]].k];
31   }
32   for (RG int i=0,v,sz=g[x].size();i<sz;++i){
33     v=g[x][i];
34     if (!dfn[v]) dfs(v,fg && dfn[x]<low[x]),low[x]=min(low[x],low[v]);
35     else if (inst[v]) low[x]=min(low[x],dfn[v]);
36   }
37   inst[x]=0,--top; return;
38 }
39 
40 int main(){
41 #ifndef ONLINE_JUDGE
42   freopen("city.in","r",stdin);
43   freopen("city.out","w",stdout);
44 #endif
45   n=gi(),m=gi(),Q=gi();
46   for (RG int i=1,u,v;i<=m;++i) u=gi(),v=gi(),g[u].push_back(v);
47   for (RG int i=1;i<=n;++i) sort(g[i].begin(),g[i].end());
48   for (RG int i=1;i<=Q;++i) q[i].i=i,q[i].u=gi(),q[i].v=gi(),q[i].k=gi();
49   sort(q+1,q+Q+1,cmp),memset(ans,-1,sizeof(ans));
50   for (RG int i=1;i<=Q;++i){
51     c[q[i].v].push_back(i); if (q[i].u==q[i+1].u) continue;
52     memset(dfn,0,sizeof(dfn)),memset(low,0,sizeof(low));
53     cnt=top=0,dfs(q[i].u,1); for (RG int j=1;j<=n;++j) c[j].clear();
54   }
55   for (RG int i=1;i<=Q;++i) printf("%d\n",ans[i]); return 0;
56 }