HDOJ 2874 Connections between cities
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原来莫名的超时,稍微改了一下就过了,还是改了的好啊。LCA的Tarjan算法,和原来是一样的,不过这是个深林不是树,所以还要用并查集确定的找到每个树的根,完后再进行Tarjan.和原来的how far away想必多了一个找树的过程。
代码:
#include<iostream>#include<string.h>using namespace std;#define maxn 10050struct Edge{ int v,w,next;} e[2*maxn],qe[2000500];bool visit[maxn];int dist[maxn],f[maxn],size,qsize,root[maxn];int head[maxn],qhead[maxn],n;void AddEdge(int a,int b,int c){ e[size].v=b; e[size].w=c; e[size].next=head[a]; head[a]=size++;}void AddQedge(int a,int b,int c){ qe[qsize].v=b; qe[qsize].w=c; qe[qsize].next=qhead[a]; qhead[a]=qsize++;}void init(){ size=0; qsize=0; memset(e,0,sizeof(e)); memset(qe,0,sizeof(qe)); memset(head,-1,sizeof(head)); memset(qhead,-1,sizeof(qhead)); memset(dist,0,sizeof(dist)); memset(root,false,sizeof(root)); for(int i=0; i<=n; i++) f[i]=i;}int Find(int x){ if( x!=f[x]) f[x]=Find(f[x]); return f[x];}void Union(int x,int y){ x=Find(x); y=Find(y); if( x!=y) f[x]=y;}void Tarjan(int u){ f[u]=u; visit[u]=true; int i; for( i=head[u]; i!=-1; i=e[i].next){ int v=e[i].v; if( !visit[v]){ dist[v]=dist[u]+e[i].w; Tarjan(v); f[v]=u; } } for( i=qhead[u]; i!=-1; i=qe[i].next){ int v=qe[i].v; if( visit[v]){ qe[i].w=dist[u]+dist[v]-2*dist[Find(v)]; qe[i^1].w=qe[i].w; } } }int main(){ int m,t,i,a,b,c,j; while( scanf("%d%d%d",&n,&m,&c)!=EOF){ init(); while( m--){ scanf("%d%d%d",&a,&b,&t); AddEdge(a,b,t); AddEdge(b,a,t); Union(a,b); } for( i=1; i<=n; i++) //找树根的过程,同时确定每个结点所在树的根节点 root[Find(i)]=true; while( c--){ scanf("%d%d",&a,&b); if( f[a]!=f[b]){ //根据原来并查之后的结果判断如果不在同一颗树上距离赋为-1. AddQedge(a,b,-1); AddQedge(b,a,-1); } else{ AddQedge(a,b,0); AddQedge(b,a,0); } } memset(f,0,sizeof(f)); for( i=1; i<=n; i++){ if( root[i]){ //如果是树根就进行遍历 memset(visit,false,sizeof(visit)); Tarjan(i); } } for( i=0; i<qsize; i+=2){ //输出距离 if( qe[i].w==-1) printf("Not connected\n"); else printf("%d\n",qe[i].w); } } return 0;}
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