hdu2856(倍增lca模版题)

Posted 2020-12-29 windfreedom

ac代码：

#include<bits/stdc++.h>
using namespace std;
#define per(i,a,b) for(int i=a;i <= b;i++)
#define Max(a,b) a=max(a,b)
#define Min(a,b) a=min(a,b)
#define Sz(x) (int)x.size()
typedef long long ll;
ll gcd(ll a,ll b){while(b){ll t=b;b=a%b;a=t;}return a;}
const int inf=0x3f3f3f3f;
const int mod=1000000007;
#define siz 40005
int T,n,m,mul_fa[siz][16],jdis[siz][16],depth[siz];//mul_fa[]表示倍增祖先，jdis[]表示向上跳2^i步的权(距离)
int head[siz],Enum=0,N;//N最多能跳的2^i个祖先,N设为log2(n)是因为就算退化成单链，根据倍增最多条log2(n)
struct node{int to,w,ne;}edge[siz*2];
void add_edge(int a,int b,int k){
    edge[Enum].to=b;
    edge[Enum].w=k;
    edge[Enum].ne=head[a];
    head[a]=Enum++;
}
void init()
{
    Enum=0;
    memset(head,-1,sizeof(head));
}
void dfs(int u,int pre)
{
    for(int i=1;i<=N;i++){
        mul_fa[u][i]=mul_fa[mul_fa[u][i-1]][i-1];
        jdis[u][i]=jdis[u][i-1]+jdis[mul_fa[u][i-1]][i-1];
    }
    for(int i=head[u];i!=-1;i=edge[i].ne){
        int v=edge[i].to;
        if(v==pre)continue;
        depth[v]=depth[u]+1;
        mul_fa[v][0]=u;
        jdis[v][0]=edge[i].w;
        dfs(v,u);
    }
}
void lca_init()
{
    N=floor((int)log2(n*1.0));
    depth[1]=0;
    memset(mul_fa,0,sizeof(mul_fa));
    memset(jdis,0,sizeof(jdis));
    dfs(1,-1);//以1为根节点建树
}
int LCA(int a,int b)
{
    if(depth[a] < depth[b])swap(a,b);
    int ans=0;
    for(int i=N;i>=0;i--){
        if(depth[a]>depth[b] && depth[a]-(1<<i)>=depth[b]){
            ans+=jdis[a][i];
            a=mul_fa[a][i];
        }
    }
    for(int i=N;i>=0;i--){
        if(mul_fa[a][i]!=mul_fa[b][i]){
            ans+=(jdis[a][i]+jdis[b][i]);
            a=mul_fa[a][i];
            b=mul_fa[b][i];
        }
    }
    if(a!=b){ans+=(jdis[a][0]+jdis[b][0]);}
    return ans;
}

int main()
{
    scanf("%d",&T);
    while(T--){
        int a,b,k;
        scanf("%d%d",&n,&m);
        init();
        for(int i=1;i<=n-1;i++){
            scanf("%d %d %d",&a,&b,&k);
            add_edge(a,b,k);add_edge(b,a,k);
        }
        lca_init();
        for(int i=1;i<=m;i++){
            scanf("%d %d",&a,&b);
            printf("%d
",LCA(a,b));
        }
    }

    return 0;
}