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  1.  
  2.     #include <bits/stdc++.h>
  3.  
  4.     using namespace std;
  5.  
  6.     using ll = long long;
  7.     const int MOD = 1000000007; 
  8.     const int MOD2 =  998244353; 
  9.     const ll INF = 1e18;
  10.     const int MX = 1000001; //check the limits, dummy
  11.  
  12.  
  13.     ll modExp(ll base, ll power) {
  14.         if (power == 0) {
  15.             return 1;
  16.         } else {
  17.             ll cur = modExp(base, power / 2); cur = cur * cur; cur = cur % MOD;
  18.             if (power % 2 == 1) cur = cur * base;
  19.             cur = cur % MOD;
  20.             return cur;
  21.         }
  22.     }
  23.  
  24.     ll inv(ll base) {
  25.         return modExp(base, MOD-2);
  26.     }
  27.  
  28.  
  29.     ll mul(ll A, ll B) {
  30.         return (A*B)%MOD;
  31.     }
  32.  
  33.     ll add(ll A, ll B) {
  34.         return (A+B)%MOD;
  35.     }
  36.  
  37.     ll dvd(ll A, ll B) {
  38.         return mul(A, inv(B));
  39.     }
  40.  
  41.     ll sub(ll A, ll B) {
  42.         return (A-B+MOD)%MOD;
  43.     }
  44.  
  45.     ll* facs = new ll[MX];
  46.     ll* facInvs = new ll[MX];
  47.  
  48.     ll choose(ll a, ll b) {
  49.         if (b > a) return 0;
  50.         if (a < 0) return 0;
  51.         if (b < 0) return 0;
  52.         ll cur = facs[a];
  53.         cur = mul(cur, facInvs[b]);
  54.         cur = mul(cur, facInvs[a-b]);
  55.         return cur;
  56.     }
  57.  
  58.     void initFacs() {
  59.         facs[0] = 1; 
  60.         facInvs[0] = 1;
  61.         for (int i = 1 ; i < MX ; i ++ ) {
  62.             facs[i] = (facs[i-1] * i) % MOD;
  63.             facInvs[i] = inv(facs[i]);
  64.         }
  65.     }
  66.     int low[100005];
  67.     int tin[100005]; 
  68.     bool isBridge[100005]; 
  69.     vector<pair<int,int>> adj[100005];
  70.     pair<int,int> edges[300005];  
  71.     int c = 1; 
  72.     void dfs(int a, int p) {
  73.         tin[a] = c; 
  74.         low[a] = c; 
  75.         c ++;
  76.         for (auto child  : adj[a]) {
  77.             if (child.first == p) continue;
  78.             if (tin[child.first] == 0) {
  79.                 dfs(child.first, a);
  80.                 low[a] =  min(low[a],low[child.first]); 
  81.                 if (low[child.first] > tin[a]) {
  82.                     isBridge[child.second] = true;
  83.                 }
  84.             } else {
  85.                 low[a] = min(low[a], tin[child.first]); 
  86.             }
  87.             edges[child.second] = {a,child.first}; 
  88.         }        
  89.     }  
  90.  
  91.     int main()  {
  92.         ios_base::sync_with_stdio(0); cin.tie(0);  
  93.         int n , m ; cin >> n >> m ;
  94.         for (int i = 0  ; i < m ; i ++) {
  95.             int a,b ; cin >> a >> b; 
  96.             adj[a].push_back({b,i});
  97.             adj[b].push_back({a,i});
  98.             edges[i] = {a,b}; 
  99.         }
  100.         for (int i = 1 ; i <= n; i ++) {
  101.             low[i] = INT_MAX;
  102.         }   
  103.         dfs(1 ,0); 
  104.  
  105.         for (int i = 0 ; i < n; i ++) {
  106.             if (isBridge[i]) {
  107.                 cout << 0 << endl;
  108.                 return 0; 
  109.             } 
  110.         }
  111.         for (int i = 0 ; i < n; i ++) {
  112.             cout << edges[0].first << ' ' << edges[0].second << endl; 
  113.         } 
  114.  
  115.         return 0;
  116.     }
  117.  
  118.  
  119.  
Success #stdin #stdout 0.01s 6100KB
comments (?)
stdin
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6 8
1 2
2 3
1 3
4 5
4 6
5 6
2 4
3 5
stdout
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1 2
1 2
1 2
1 2
1 2
1 2
https://ideone.com/XSqKr1
language:
C++ (gcc 8.3)
created:
10 days ago
visibility:
public

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