LCA
题意:询问LCA,不过图不连通,如果两点不连通输出那串英文否则输出两点间的距离,模板题
#include <iostream> #include <cstdio> #include <cstring> using namespace std; #define N 10010 #define M 10010 #define Q 1000010 int head[N]; struct edge{ int u,v,w,next; }e[2*M]; int __head[N]; struct ask{ int u,v,lca,next; }ea[2*Q]; int dir[N],fa[N],vis[N]; inline void add_edge(int u ,int v ,int w ,int &k) { e[k].u = u; e[k].v = v; e[k].w = w; e[k].next = head[u]; head[u] = k++; } inline void add_ask(int u ,int v ,int &k) { ea[k].u = u; ea[k].v = v; ea[k].lca = -1; ea[k].next = __head[u]; __head[u] = k++; } int find(int x){ return x == fa[x] ? x : fa[x] = find(fa[x]); } void Tarjan(int u ,int c) { vis[u] = c; fa[u] = u; for(int k=head[u]; k!=-1; k=e[k].next) if(!vis[e[k].v]) { int v = e[k].v , w = e[k].w; dir[v] = dir[u] + w; Tarjan(v,c); fa[v] = u; } for(int k=__head[u]; k!=-1; k=ea[k].next) if(vis[ea[k].v] == c) ea[k].lca = ea[k^1].lca = find(ea[k].v); } int main() { int n,m,q,k; while(scanf("%d%d%d",&n,&m,&q)!=EOF) { memset(head,-1,sizeof(head)); memset(__head,-1,sizeof(__head)); memset(vis,0,sizeof(vis)); k = 0; for(int i=0; i<m; i++) { int u,v,w; scanf("%d%d%d",&u,&v,&w); add_edge(u,v,w,k); add_edge(v,u,w,k); } k = 0; for(int i=0; i<q; i++) { int u,v; scanf("%d%d",&u,&v); add_ask(u,v,k); add_ask(v,u,k); } k = 0; for(int i=1; i<=n; i++) if(!vis[i]) { dir[i] = 0; Tarjan(i,++k); } for(int i=0; i<q; i++) { int s = i*2 , u = ea[s].u , v = ea[s].v , lca = ea[s].lca; if(lca == -1) printf("Not connected\n"); else printf("%d\n",dir[u] + dir[v] - 2*dir[lca]); } } return 0; }