• E 旗鼓相当的对手


    题:https://ac.nowcoder.com/acm/contest/4853/E

    题意:对于一对点(u,v)要是dis(u,v)==k,就会对这对点的LCA产生a[x]+a[y]的贡献(LCA!=u&&LCA!=v)

    分析:简单的dsu,把每个点当作LCA去统计子树深度个数,经过LCA的路径就是深度之和;

       对于每个点u深度对应要达成k的深度要为2*deep[LCA]-deep[u]+k;

    #include<bits/stdc++.h>
    using namespace std;
    #define pb push_back
    typedef long long ll;
    const int M=2e5+5;
    ll ans[M];
    ll val[M],sz[M],son[M],a[M],cnt[M],deep[M];
    ll k,n;
    vector<ll>g[M];
    ll nownum;
    void dfs1(ll u,ll fa){
        sz[u]=1;
        for(auto v:g[u]){
            if(v!=fa){
                deep[v]=deep[u]+1;
                dfs1(v,u);
                sz[u]+=sz[v];
                if(sz[v]>sz[son[u]])
                    son[u]=v;
            }
        }
    }
    
    void add(ll u,ll fa,ll x){
        cnt[deep[u]]+=x;
        val[deep[u]]+=x*a[u];
        for(auto v:g[u]){
            if(v!=fa)
                add(v,u,x);
        }
    }
    void cal(ll u,ll fa,ll LCA){
        ll need=k+deep[LCA]*2-deep[u];
        if(need>0){
            nownum+=val[need];
            nownum+=cnt[need]*a[u];
        }
        for(auto v:g[u])
            if(v!=fa)
                cal(v,u,LCA);
    }
    void dfs2(ll u,ll fa,ll sign){
        //cout<<u<<endl;
        for(auto v:g[u]){
            if(v!=fa&&son[u]!=v)
                dfs2(v,u,0);
        }
        if(son[u])
            dfs2(son[u],u,1);
        for(auto v:g[u])
            if(v!=fa&&v!=son[u])
                cal(v,u,u),add(v,u,1);
        ans[u]=nownum;
        cnt[deep[u]]++,val[deep[u]]+=a[u];
        if(!sign)
            add(u,fa,-1);
        nownum=0;
    
    }
    int main(){
        scanf("%lld%lld",&n,&k);
        for(ll i=1;i<=n;i++)
            scanf("%lld",&a[i]);
        for(ll u,v,i=1;i<n;i++){
            scanf("%lld%lld",&u,&v);
            g[u].pb(v);
            g[v].pb(u);
        }
        dfs1(1,0);
    
        dfs2(1,0,1);
        for(ll i=1;i<=n;i++)
            printf("%lld ",ans[i]);
        return 0;
    }
    View Code
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  • 原文地址:https://www.cnblogs.com/starve/p/12597621.html
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