Codevs 2370 小机房的树

http://codevs.cn/problem/2370/

倍增LCA版本

代码

#include<iostream>#include<cstdio>#include<cmath>#include<cstring>#include<algorithm>using namespace std;int n,m,u,v,c,tot;int next[50001*2],first[50001],deep[50001],rank[50001],anc[50001][25];struct edge{    int t;    int d;}l[100001];void build(int u,int v,int c){    l[++tot].t=v;    l[tot].d=c;    next[tot]=first[u];    first[u]=tot;}void dfs(int u,int fa,int w){    deep[u]=deep[fa]+1;    anc[u][0]=fa;    rank[u]=w;    for(int i=1;anc[u][i-1];i++)    {        anc[u][i]=anc[anc[u][i-1]][i-1];    }    for(int i=first[u];i!=-1;i=next[i])//for(int i=first[u];i;i=next[i])i不为0     {        int v=l[i].t;        if(!deep[v])        {            dfs(v,u,w+l[i].d);        }    }}int ask_lca(int x,int y){    if(deep[x]<deep[y]) swap(x,y);    if(deep[x]>deep[y])    {        int dd=deep[x]-deep[y];        for(int i=0;i<=20;i++)        {            if(dd&(1<<i))            {                x=anc[x][i];            }        }    }    if(x!=y)    {        for(int i=20;i>=0;i--)        {            if(anc[x][i]!=anc[y][i])            {                x=anc[x][i];                y=anc[y][i];            }        }    }    if(x==y) return x;    else return anc[x][0];}int main(){    memset(first,-1,sizeof(first));    scanf("%d",&n);    for(int i=1;i<=n-1;i++)    {        scanf("%d%d%d",&u,&v,&c);        build(u,v,c);        build(v,u,c);    }    dfs(0,0,0);    scanf("%d",&m);    for(int i=1;i<=m;i++)    {        scanf("%d%d",&u,&v);        printf("%d\n",rank[u]+rank[v]-(2*rank[ask_lca(u,v)]));    }    return 0;}

树链剖分版本

代码

#include<iostream>#include<cstdio>#include<algorithm>#include<cstring>#include<cmath>using namespace std;typedef long long ll;int n,m,ru,rv,rw,a,b,tot;int first[1000010],nxt[1000010],deep[1000010],f[1000010],top[1000010],siz[1000010],son[1000010],rank[1000010];struct edge{    int u,v,w;}l[1000010];void add(int f,int t,int c){    l[++tot]=(edge){f,t,c};    nxt[tot]=first[f];    first[f]=tot;}void dfs_1(int k,int fa,int d){    deep[k]=d;    f[k]=fa;    siz[k]=1;    for(int i=first[k];i!=-1;i=nxt[i])    {        int x=l[i].v;        if(x==fa)        continue;        dfs_1(x,k,d+1);        siz[k]+=siz[x];        if(!son[k]||siz[x]>siz[son[k]])        son[k]=x;    }}void dfs_2(int k,int num){    top[k]=num;    if(!son[k])    return;    dfs_2(son[k],num);    for(int i=first[k];i!=-1;i=nxt[i])    {        int x=l[i].v;        if(x!=son[k]&&x!=f[k])        dfs_2(x,x);    }}void dfs(int k,int d){    rank[k]=d;    for(int i=first[k];i!=-1;i=nxt[i])    {        int x=l[i].v;        if(x!=f[k])        dfs(x,d+l[i].w);    }}ll find_lca(int x,int y){    int f1=top[x],f2=top[y];    ll ans=0;    while(f1!=f2)    {        if(deep[f1]<deep[f2])        {            f1=f1^f2;            f2=f1^f2;            f1=f1^f2;            x=x^y;            y=x^y;            x=x^y;        }        ans+=rank[x]-rank[f[f1]];//注意边界问题         x=f[f1];        f1=top[x];    }    if(deep[x]>deep[y])    ans+=rank[x]-rank[y];    if(deep[y]>=deep[x])    ans+=rank[y]-rank[x];    return ans;}int main(){    memset(first,-1,sizeof(first));    scanf("%d",&n);    for(int i=1;i<n;i++)    {        scanf("%d%d%d",&ru,&rv,&rw);        add(ru,rv,rw);        add(rv,ru,rw);    }    tot=0;    dfs_1(0,0,1);    dfs_2(0,0);    dfs(0,0);    scanf("%d",&m);    for(int i=1;i<=m;i++)    {        scanf("%d%d",&a,&b);        printf("%lld\n",find_lca(a,b));    }    return 0;}