UVA OJ - 796, Bridge finding

2017/critical.cpp

+#include <cstdio>
+#include <algorithm>
+#include <vector>
+
+#define X first
+#define Y second
+#define mp make_pair
+#define pb push_back
+
+using namespace std;
+
+typedef pair< int, int > pii;
+
+int N, cnt = 0;
+
+vector< vector< int > > G;
+vector< int > low, time, visited;
+vector< pii > bridges;
+
+void dfs( int u, int p ) {
+  time[ u ] = ++cnt;
+  low[ u ] = time[ u ];
+  for( int i = 0; i < G[ u ].size(); i++ ) {
+    int v = G[ u ][ i ];
+    if( v == p ) continue;
+    if( !time[ v ] ) {
+      dfs( v, u );
+      if( time[ u ] < low[ v ] ) bridges.pb( mp( min( u, v ), max( u, v ) ) );
+      low[ u ] = min( low[ u ], low[ v ] );
+    } else {
+      low[ u ] = min( low[ u ], time[ v ] );
+    }
+  }
+}
+
+int main( void ) {
+  while( scanf("%d", &N ) == 1 ) {
+    G.resize( N + 1 );
+    low.resize( N + 1, 0 );
+    time.resize( N + 1, 0 );
+
+    for( int i = 0; i < N; i++ ) {
+      int u, e, v;
+      scanf("%d (%d)", &u, &e );
+
+      for( int j = 0; j < e; j++ ) {
+        scanf("%d", &v );
+        G[ u ].pb( v );
+      }
+    }
+
+    for( int i = 0; i < N; i++ ) {
+      if( !time[ i ] ) dfs( i, -1 );
+    }
+    sort( bridges.begin(), bridges.end() );
+    printf("%d critical links\n", bridges.size() );
+    for( int i = 0; i < bridges.size(); i++ ) {
+      printf("%d - %d\n", bridges[ i ].X, bridges[ i ].Y );
+    }
+
+    printf("\n");
+
+    cnt = 1;
+    bridges.clear();
+    for( int i = 0; i < N; i++ ) G[ i ].clear();
+    low.clear();
+    time.clear();
+  }
+  return 0;
+}