Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

Code mẫu của ladpro98

#include <iostream>
#include <stdio.h>
#include <cstdio>
#define maxn 10001

int adj[maxn], adj2[maxn], head[maxn], head2[maxn], linker[maxn], link2[maxn], part[maxn];
bool avail[maxn], visit[maxn];
int res,n,m,t,ssc;

using namespace std;

void inputer() {
    //freopen("number.in","r",stdin);
    scanf("%d %d %d", &n, &m, &t);
    int x,y;
    for(int i=1; i<=m; i++) {
        scanf("%d %d", &x, &y);
        adj[i] = y;
        linker[i] = head[x];
        head[x] = i;
        adj2[i] = x;
        link2[i] = head2[y];
        head2[y] = i;
    }
}

int dfser(int i) {
    avail[i] = false;
    int j = head[i];
    while (j) {
        if (avail[adj[j]]) return dfser(adj[j]);
        j = linker[j];
    }
    return i;
}

void dfs2(int i) {
    visit[i] = true;
    int j = head2[i];
    while (j) {
        if (!visit[adj2[j]])
            dfs2(adj2[j]);
        j = link2[j];
    }
}

void dfsFind(int i) {
    visit[i] = true;
    avail[part[i]] = false;
    int j = head2[i];
    while (j) {
        if (!visit[adj2[j]])
            dfsFind(adj2[j]);
        j = link2[j];
    }
}

void process() {
    for(int i=1; i<=n; i++)
    {
        avail[i] = true;
        visit[i] = false;
    }
    int st;
    for(int i=1; i<=n; i++) {
        if (!visit[i]) {
            st = dfser(i);
            ssc++;
            part[st] = ssc;
            dfs2(st);
        }
    }
    for(int i=1; i<=n; i++) {
            visit[i] = false;
            avail[i] = true;
    }
    dfsFind(t);
    for(int i=1; i<=ssc; i++)
        if (avail[i]) res++;
}

void outputer() {
    printf("%d",res);
}

int main()
{
    inputer();
    process();
    outputer();
    return 0;
}

Code mẫu của RR

//Written by RR

{$MODE OBJFPC}

uses math;
const
  FINP          =       '';
  FOUT          =       '';
  MAXN          =       10111;

type
  list          =       ^node;
  node          =       record
        u       :       longint;
        next    :       list;
  end;

procedure add(u:longint; var a:list);
    var
      p:list;
    begin
      new(p); p^.u:=u;
      p^.next:=a; a:=p;
    end;

var
  f1,f2         :       text;

  //Input
  m,n,t         :       longint;
  ke            :       array[1..MAXN] of list;

  vao,ra,dd     :       array[1..MAXN] of longint;
  hsize         :       longint;
  h,hpos        :       array[1..MAXN] of longint;

procedure openF;
    begin
      assign(f1,FINP); reset(f1);
      assign(f2,FOUT); rewrite(f2);
    end;

procedure closeF;
    begin
      close(f1);
      close(f2);
    end;

procedure inp;
    var
      i,u,v:longint;
    begin
      read(f1,n,m,t);
      for i:=1 to m do
        begin
          read(f1,u,v);
          if u=v then continue;
          add(u,ke[v]);
          inc(ra[v]);
          inc(vao[u]);
        end;
    end;

procedure swap(var a,b:longint);
    var
      tmp:longint;
    begin
      tmp:=a; a:=b; b:=tmp;
    end;

procedure swaph(var a,b:longint);
    begin
      swap(hpos[h[a]],hpos[h[b]]);
      swap(h[a],h[b]);
    end;

function lower(a,b:longint):boolean;
    begin
      exit( vao[h[a]] < vao[h[b]] );
    end;

procedure down(i:longint);
    var
      j:longint;
    begin
      j:=i shl 1;
      while (j<=hsize) do
        begin
          if (j<hsize) and lower(j+1,j) then inc(j);
          if lower(j,i) then swaph(i,j);
          i:=j; j:=i shl 1;
        end;
    end;

procedure up(i:longint);
    var
      j:longint;
    begin
      j:=i shr 1;
      while (i>1) and lower(i,j) do
        begin
          swaph(i,j);
          i:=j; j:=i shr 1;
        end;
    end;

procedure push(u:longint);
    begin
      inc(hsize); h[hsize]:=u; hpos[u]:=hsize;
      up(hsize);
    end;

procedure pop(var u:longint);
    begin
      u:=h[1]; hpos[u]:=0;
      h[1]:=h[hsize]; hpos[h[1]]:=1; dec(hsize);
      down(1);
    end;

procedure dfs(u:longint);
    var
      v:longint;
      p:list;
    begin
      dd[u]:=1;
      p:=ke[u];
      while p<>nil do
        begin
          v:=p^.u; p:=p^.next;
          if dd[v]=0 then dfs(v);
        end;
    end;

procedure solve;
    var
      i,u,v,res:longint;
      p:list;
    begin
      for i:=1 to n do
        push(i);

      res:=0;
      dfs(t);
      for i:=1 to n do
        begin
          pop(u);
          if (u<>t) and (dd[u]=0) then inc(res);
          dfs(u);
        end;
      writeln(f2,res);
    end;

begin
  openF;
  inp;
  solve;
  closeF;
end.

Code mẫu của hieult

#include<cstdio>
#include<cmath>
#include<cstring>
#include<cstdlib>
#include<cassert>
#include<ctime>
#include<algorithm>
#include<iterator>
#include<iostream>
#include<cctype>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<list>
//#include<conio.h>
#define ep 0.000000001
//#define maxn 222
#define oo 1111111111
#define base 100000000
#define TR(c, it) for(typeof((c).begin()) it=(c).begin(); it!=(c).end(); it++)
double const PI=4*atan(1);
int const maxn = 10003;

using namespace std;

//NUMBER


struct CANH{
     int u,v;
};

    int a[maxn],n,m,t,u,v,KQ;
    CANH c[maxn];
    int coun[maxn],head[maxn];
    bool f[maxn];

void BFS(int u){
          int v;
          f[u] = false;
          for(int i=head[u];i<=head[u+1]-1;i++) {
                        v = a[i];
                        if(f[v]) BFS(v);
          }
}

int main(){   
//freopen("NUMBER.in","r",stdin);
scanf("%d %d %d",&n,&m,&t);

for(int i = 1;i<=m;i++){
        scanf("%d %d",&c[i].v,&c[i].u);
        coun[c[i].u]++;
}
f[1] = true;
head[1] = 1;
head[n+1] = m+1;
for(int i = 2;i<=n;i++){
         head[i] = head[i-1]+coun[i-1];
         f[i] = true;
}
for(int i = 1;i<=m;i++){
         u = c[i].u;
         v = c[i].v;
         coun[u]--;
         a[head[u]+coun[u]] = v;
}
BFS(t);
for(int i = 1;i<=n;i++)
    if(f[i]){
            BFS(i);
            f[i] =true;
}
for( int i  = 1;i<=n;i++)
    if (f[i]) KQ++;
printf("%d",KQ);
//getch();
}

Code mẫu của khuc_tuan

#include <iostream>
#include <vector>
#include <stack>
using namespace std;

int n, m, T;
vector<int> ds[11000];
bool vs[11000], visiting[11000];
stack<int> st;
int low[11000], num[11000], dem = 0;
int tp[11000], sotp = 0;
bool mark[11000];

void dfs(int i) {
    visiting[i] = true;
    st.push(i);
    vs[i] = true;
    low[i] = num[i] = ++dem;
    for(int k=0;k<ds[i].size();++k) {
        int j = ds[i][k];
        if(!vs[j]) {
            dfs(j);
            low[i] <?= low[j];
        }   
        else if(visiting[j]) low[i] <?= num[j];
    }
    if(low[i] == num[i]) {
        ++ sotp;
        while(true) {
            int u = st.top();
            st.pop();
            tp[u] = sotp;
            if(u==i) break;
        }
    }
    visiting[i] = false;
}

int main() {
    scanf("%d%d%d", &n, &m, &T);    
    for(int i=0;i<m;++i) {
        int u, v;
        scanf("%d%d", &u, &v);
        ds[u].push_back(v); 
    }
    // cout << "??" << endl;
    for(int i=1;i<=n;++i) if(!vs[i]) dfs(i);
    for(int i=1;i<=n;++i) for(int k=0;k<ds[i].size();++k) {
        int j = ds[i][k];
        if(tp[i] != tp[j]) {
            mark[tp[i]] = true;
        }
    }
    int result = 0;
    for(int i=1;i<=sotp;++i) if(!mark[i] && i!=tp[T]) ++result;
    cout << result << endl;
    return 0;
}