#include<cstdio> #include<cstring> #include<cmath> #include<algorithm> #include<vector> using namespace std; const int maxn = 101000; vector<int> mp[maxn]; int dfn[maxn],low[maxn],pre[maxn],p[maxn],cnt,ans; int find(int u){ return u == pre[u]?u:(pre[u] = find(pre[u])); } int unio(int u,int v){ int t1 = find(u); int t2 = find(v); if(t1 == t2) return 0; pre[t1] = t2; return 1; } void Tarjan(int u,int fa){ dfn[u] = low[u] = ++cnt; for( int i = 0; i < mp[u].size(); i++){ int v = mp[u][i]; if(v == fa) continue; if(!dfn[v]){ p[v] = u; Tarjan(v,u); low[u] = min(low[u],low[v]); if(low[v] > dfn[u]){ ans++; }else unio(u,v); }else{ low[u] = min(low[u],dfn[v]); } } } void lca(int u,int v){ if(dfn[v] < dfn[u]) swap(v,u); while(dfn[v] > dfn[u]){ if(unio(v,p[v])) ans--; v = p[v]; } while(v != u){ if(unio(u,p[u])) ans--; u = p[u]; } } int main(){ int n,m,q,u,v,t=1; while(scanf("%d%d",&n,&m) == 2 && m+n){ ans = cnt = 0; for( int i = 0; i <= n; i++){ pre[i] = i; } while(m--){ scanf("%d%d",&u,&v); mp[u].push_back(v); mp[v].push_back(u); } p[1] = 1; Tarjan(1,1); scanf("%d",&q); printf("Case %d:\n",t++); while(q--){ scanf("%d%d",&u,&v); lca(u,v); printf("%d\n",ans); } printf("\n"); } return 0; }
给定一个连通图 q个询问 每次加一条边 每次求出有多少个桥 poj 3694
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