HDU 2874 Connections between cities 【LCA】

在线 lca ：

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<math.h>
#include<iostream>
#include<stdlib.h>
#include<set>
#include<map>
#include<queue>
#include<stack>
#include<vector>
#include<bitset>
#pragma comment(linker, "/STACK:1024000000,1024000000")
template <class T>
bool scanff(T &ret){
    char c; int sgn; T bit=0.1;
    if(c=getchar(),c==EOF) return 0;
    while(c!='-'&&c!='.'&&(c<'0'||c>'9')) c=getchar();
    sgn=(c=='-')?-1:1;
    ret=(c=='-')?0:(c-'0');
    while(c=getchar(),c>='0'&&c<='9') ret=ret*10+(c-'0');
    if(c==' '||c=='\n'){ ret*=sgn; return 1; }
    while(c=getchar(),c>='0'&&c<='9') ret+=(c-'0')*bit,bit/=10;
    ret*=sgn;
    return 1;
}
#define inf 1073741824
#define llinf 4611686018285162540LL
#define eps 1e-8
#define mod 9223372034707292160LL
#define pi acos(-1.0)
#define lth (th<<1)
#define rth (th<<1|1)
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define drep(i,a,b) for(int i=a;i>=b;i--)
#define mset(x,val) memset(x,val,sizeof(x))
#define mcpy(x,y) memcpy(x,y,sizeof(y))
#define findx(x) lower_bound(b+1,b+1+bn,x)-b
#define mpii(a,b) make_pair(a,b);
#define NN 101010
#define MM 202020
using namespace std;
typedef long long ll;
typedef long double lb;
typedef pair<int,int> pii;
int n,m,q;
struct Edge{
    int to,val,nx;
    Edge(){}
    Edge(int t,int v,int n){
        to=t,val=v,nx=n;
    }
}ed[MM];

int start[11111],lm,fa[11111],root[11111],dis[11111],deep[11111],totr;
void init(){
    mset(start,-1);
    mset(fa,0);
    lm=0;
}

void add(int x,int y,int v){
    ed[lm]=Edge(y,v,start[x]);
    start[x]=lm++;
}

void dfs(int s,int f,int de,int di){
    root[s]=totr;
    deep[s]=de;
    dis[s]=di;
    fa[s]=f;
    for(int i=start[s];~i;i=ed[i].nx){
        Edge& e=ed[i];
        if(fa[e.to]==0) dfs(e.to,s,de+1,di+e.val);
    }
}

int lca(int x,int y){
    if(x==y) return x;
    if(deep[x]>deep[y]) swap(x,y);
    return lca(x,fa[y]);
}

int main(){
    while(scanf("%d%d%d",&n,&m,&q)!=EOF){
        init();
        rep(i,1,m){
            int u,v,w;
            scanff(u);
            scanff(v);
            scanff(w);
            add(u,v,w);
            add(v,u,w);
        }

        rep(i,1,n){
            if(fa[i]==0){
                totr=i;
                dfs(i,-1,1,0);
            }
        }

        rep(i,1,q){
            int a,b;
            scanff(a);
            scanff(b);
            if(root[a]==root[b]){
                int ace=lca(a,b);
                printf("%d\n",dis[a]+dis[b]-2*dis[ace]);
            }
            else printf("Not connected\n");
        }

    }
    return 0;
}

离线lca：

#include<stdio.h>
#include<string.h>
#include<algorithm>
#define MM 2002000
#define NN 20020
using namespace std;
struct node{
    int gopos,nxt,cost;
}cc[NN];
struct qnode{
    int gopos,nxt,index;
}qc[MM];
int start[NN],qstart[NN],fa[NN],vis[NN],dis[NN],ans[MM],n,m,q,lnum,tot;
inline void add(int u,int v,int w){
    lnum++,cc[lnum].gopos=v,cc[lnum].cost=w,cc[lnum].nxt=start[u],start[u]=lnum;
}
inline void qadd(int u,int v,int pos){
    tot++,qc[tot].gopos=v,qc[tot].index=pos,qc[tot].nxt=qstart[u],qstart[u]=tot;
}
int Find(int x){
    if(fa[x]!=x)
        fa[x]=Find(fa[x]);
    return fa[x];
}
void init(){
    lnum=tot=0;                                     
    memset(vis,0,sizeof(vis));
    memset(start,-1,sizeof(start));
    memset(qstart,-1,sizeof(qstart));
    for(int i=1;i<=q;i++) ans[i]=-1;            
}
void Tarjan(int s,int root){
    vis[s]=root,fa[s]=s;
    for(int i=start[s];i!=-1;i=cc[i].nxt){
        int y = cc[i].gopos;
        if(!vis[y]){
            dis[y]=dis[s]+cc[i].cost; 
            Tarjan(y,root);fa[y]=s;    
        }
    }
    for(int i=qstart[s];i!=-1;i=qc[i].nxt){
        int y = qc[i].gopos;
        if(vis[y]==root){                               
            ans[qc[i].index]=dis[y]+dis[s]-2*dis[Find(y)];
        }
    }
}
int main(){
    int u,v,w;
    while(scanf("%d%d%d",&n,&m,&q)!=EOF){
        init();    
        for(int i=1;i<=m;i++){
            scanf("%d%d%d",&u,&v,&w);
            add(u,v,w);add(v,u,w);
        }
        for(int i=1;i<=q;i++){
            scanf("%d%d",&u,&v);
            qadd(u,v,i);qadd(v,u,i);
        }
        for(int i=1;i<=n;i++) if(!vis[i]) dis[i]=0,Tarjan(i,i);
        for(int i=1;i<=q;i++){
            if(ans[i]==-1) printf("Not connected\n");
            else printf("%d\n",ans[i]);
        }
    }
    return 0;
}