codeforces 757F Team Rocket Rises Again

  1 //It is made by wfj_2048~
  2 #include <algorithm>
  3 #include <iostream>
  4 #include <complex>
  5 #include <cstring>
  6 #include <cstdlib>
  7 #include <cstdio>
  8 #include <vector>
  9 #include <cmath>
 10 #include <queue>
 11 #include <stack>
 12 #include <map>
 13 #include <set>
 14 #define inf (1LL<<60)
 15 #define M (300010)
 16 #define N (200010)
 17 #define il inline
 18 #define RG register
 19 #define ll long long
 20 #define File(s) freopen(s".in","r",stdin),freopen(s".out","w",stdout)
 21 
 22 using namespace std;
 23 
 24 struct edge{ int nt,to; ll dis; }g[2*M],g1[2*M],g2[2*M];
 25 
 26 int head[N],head1[N],head2[N],q[20*N],d[N],vis[N],dep[N],sz[N],f[22][N],S,n,m,num,num1,num2,ans;
 27 ll dis[N];
 28 
 29 il int gi(){
 30     RG int x=0,q=1; RG char ch=getchar(); while ((ch<‘0‘ || ch>‘9‘) && ch!=‘-‘) ch=getchar();
 31     if (ch==‘-‘) q=-1,ch=getchar(); while (ch>=‘0‘ && ch<=‘9‘) x=x*10+ch-48,ch=getchar(); return q*x;
 32 }
 33 
 34 il void insert(RG int from,RG int to,RG ll dis){ g[++num]=(edge){head[from],to,dis},head[from]=num; return; }
 35 
 36 il void insert1(RG int from,RG int to){ g1[++num1]=(edge){head1[from],to},head1[from]=num1; return; }
 37 
 38 il void insert2(RG int from,RG int to){ g2[++num2]=(edge){head2[from],to},head2[from]=num2; return; }
 39 
 40 il void spfa(RG int S){
 41     for (RG int i=1;i<=n;++i) dis[i]=inf;
 42     RG int h=0,t=1; dis[S]=0,vis[S]=1,q[t]=S;
 43     while (h<t){
 44     RG int x=q[++h];
 45     for (RG int i=head[x],v=g[i].to;i;i=g[i].nt,v=g[i].to)
 46         if (dis[v]>dis[x]+g[i].dis){
 47         dis[v]=dis[x]+g[i].dis;
 48         if (!vis[v]) vis[v]=1,q[++t]=v;
 49         }
 50     vis[x]=0;
 51     }
 52     return;
 53 }
 54 
 55 il void dfs1(RG int x){
 56     vis[x]=1;
 57     for (RG int i=head[x],v=g[i].to;i;i=g[i].nt,v=g[i].to)
 58     if (dis[v]==dis[x]+g[i].dis){
 59         insert1(x,v),insert2(v,x),d[v]++;
 60         if (!vis[v]) dfs1(v);
 61     }
 62     return;
 63 }
 64 
 65 il void dfs2(RG int x){
 66     sz[x]=1; RG int v;
 67     for (RG int i=head[x];i;i=g[i].nt)
 68     v=g[i].to,dfs2(v),sz[x]+=sz[v];
 69     if (x!=S) ans=max(ans,sz[x]); return;
 70 }
 71 
 72 il int lca(RG int u,RG int v){
 73     if (u==v) return u; if (dep[u]<dep[v]) swap(u,v);
 74     for (RG int i=20;i>=0;--i)
 75     if (dep[f[i][u]]>=dep[v]) u=f[i][u];
 76     if (u==v) return u;
 77     for (RG int i=20;i>=0;--i)
 78     if (f[i][u]!=f[i][v]) u=f[i][u],v=f[i][v];
 79     return f[0][u];
 80 }
 81 
 82 il void topsort(){
 83     RG int h=0,t=1; q[t]=S,dep[S]=1; //不赋初值会跪烂！！！
 84     while (h<t){
 85     RG int x=q[++h],v;
 86     for (RG int i=head1[x];i;i=g1[i].nt){
 87         v=g1[i].to,d[v]--;
 88         if (!d[v]){
 89         q[++t]=v; RG int Lca=0;
 90         for (RG int j=head2[v];j;j=g2[j].nt)
 91             if (!Lca) Lca=g2[j].to; else Lca=lca(Lca,g2[j].to);
 92         insert(Lca,v,0),f[0][v]=Lca,dep[v]=dep[Lca]+1;
 93         for (RG int j=1;j<=20;++j) f[j][v]=f[j-1][f[j-1][v]];
 94         }
 95     }
 96     }
 97     return;
 98 }
 99 
100 il void work(){
101     n=gi(),m=gi(),S=gi();
102     for (RG int i=1,u,v,w;i<=m;++i){
103     u=gi(),v=gi(),w=gi();
104     insert(u,v,(ll)w),insert(v,u,(ll)w);
105     }
106     spfa(S); dfs1(S); memset(head,0,sizeof(head)),num=0;
107     topsort(); dfs2(S); printf("%d\n",ans); return;
108 }
109 
110 int main(){
111     File("757F");
112     work();
113     return 0;
114 }