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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define FOR(i,a,b) for (int i=(a),_b=(b);i<=_b;i=i+1)
  4. #define FORD(i,b,a) for (int i=(b),_a=(a);i>=_a;i=i-1)
  5. #define REP(i,n) for (int i=0,_n=(n);i<_n;i=i+1)
  6. #define FORE(i,v) for (__typeof((v).begin()) i=(v).begin();i!=(v).end();i++)
  7. #define ALL(v) (v).begin(),(v).end()
  8. #define pb push_back
  9. #define mp make_pair
  10. #define fi first
  11. #define se second
  12. #define SZ(x) ((int)(x).size())
  13. #define double db
  14. typedef long long ll;
  15. typedef pair<int,int> PII;
  16. const ll mod=1000000007;
  17. ll powmod(ll a,ll b) {ll res=1;a%=mod; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
  18. const int MAXN = 1E4+3;
  19. const int oo = 1e9+3;
  20.  
  21. int n, m, s, u, v, res, bac[MAXN],adj[MAXN][MAXN];
  22. bool ok[MAXN];
  23. queue<int> q;
  24. vector<int> a[MAXN];
  25.  
  26. int main() {
  27.     	#ifndef ONLINE_JUDGE
  28.     	freopen("test.inp", "r", stdin);
  29.     	freopen("test.out", "w", stdout);
  30.     	#endif
  31.     cin >> n >> m >> s;
  32.     FOR(i,1,m) {
  33.         cin >> u >> v;
  34.         if (!adj[u][v])
  35.             a[u].push_back(v);
  36.         adj[u][v] = 1;
  37.     }
  38.     q.push(s); bac[s] = 1;
  39.     while (!q.empty()) {
  40.         u = q.front();
  41.         q.pop();
  42.         for(int i=0; i<a[u].size(); i++)
  43.         {
  44.             v = a[u][i];
  45.             if (!bac[v])
  46.             {
  47.                 if (ok[u]) ok[v] = 1;
  48.                 bac[v] = bac[u] + 1;
  49.                 q.push(v);
  50.             }
  51.             else
  52.             if (bac[v] == bac[u] + 1) ok[v] = 1;
  53.         }
  54.     }
  55.     FOR(i,1,n) if (ok[i]) res++;
  56.     cout << res;
  57. 	return 0;
  58. }
  59.  
Success #stdin #stdout 0s 407232KB
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https://ideone.com/AQF1wp
problem STABLE, based on SPOJ submission 19972487 (CPP14), 2017-08-15 06:32:46
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
secret

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