SP3978 DISQUERY - Distance Query

Posted 2020-11-29 qyj060604

SP3978 DISQUERY - Distance Query

LCA高级水题

倍增搞一搞即可

代码：

#include<bits/stdc++.h>
using namespace std;
const int N=100005;
int n,m;
int hed[N<<1],tal[N<<1],val[N<<1],nxt[N<<1],cnt=0;
int Start[N],End[N];
int dep[N]={0};
int f[N][30];
int maxn[N][30];
int minn[N][30];
void addege(int x,int y,int z){
    cnt++;
    tal[cnt]=y;
    val[cnt]=z;
    nxt[cnt]=hed[x];
    hed[x]=cnt;
}
void dfs(int u,int father){
    f[u][0]=father;
    for(int i=hed[u];i;i=nxt[i]){
        int v=tal[i];
        if(v==father) continue;
        dep[v]=dep[u]+1;
        maxn[v][0]=val[i];
        minn[v][0]=val[i];
        dfs(v,u);
    }
}
int LCA1(int u,int v){
    int ans=2147483647;
    if(dep[u]<dep[v]) swap(u,v);
    for(int i=28;i>=0;i--) if(dep[f[u][i]]>=dep[v]) ans=min(ans,minn[u][i]),u=f[u][i];
    if(u==v) return ans;
    for(int i=28;i>=0;i--) if(f[u][i]!=f[v][i]) ans=min(ans,minn[u][i]),ans=min(ans,minn[v][i]),u=f[u][i],v=f[v][i];
    ans=min(ans,min(minn[u][0],minn[v][0]));
    return ans;
}
int LCA2(int u,int v){
    int ans=-2147483647;
    if(dep[u]<dep[v]) swap(u,v);
    for(int i=28;i>=0;i--) if(dep[f[u][i]]>=dep[v]) ans=max(ans,maxn[u][i]),u=f[u][i];
    if(u==v) return ans;
    for(int i=28;i>=0;i--) if(f[u][i]!=f[v][i]) ans=max(ans,maxn[u][i]),ans=max(ans,maxn[v][i]),u=f[u][i],v=f[v][i];
    ans=max(ans,max(maxn[u][0],maxn[v][0]));
    return ans;
}
int main(){
    memset(minn,127,sizeof(minn));
    memset(maxn,128,sizeof(maxn));
    scanf("%d",&n);
    for(int i=1;i<n;i++){
        int x,y,z;
        scanf("%d%d%d",&x,&y,&z);
        addege(x,y,z);
        addege(y,x,z);
    }
    dep[1]=1;
    dfs(1,1);
    for(int j=1;j<=28;j++){
        for(int i=1;i<=n;i++){
            f[i][j]=f[f[i][j-1]][j-1];
            maxn[i][j]=max(maxn[i][j-1],maxn[f[i][j-1]][j-1]);
            minn[i][j]=min(minn[i][j-1],minn[f[i][j-1]][j-1]);
        }
    }
    scanf("%d",&m);
    while(m--){
        int u,v;
        scanf("%d%d",&u,&v);
        printf("%d %d
",LCA1(u,v),LCA2(u,v));
    }
    return 0;
}