NOIP 模拟 $17; m weight$

题解 (by;zjvarphi)

一道树剖的题

先对于原图求出一棵最小生成树，求出来的这棵树中的边定为树边，其它边叫非树边

那么对于一条非树边，它要成为最小生成树上的边，权值只能为连接它两个端点的树上路径最小值减 (1)，因为，他和这些树边构成了一个环，最小生成树要在环上去掉最大的一条边，所以只要这条边比树上路径最大值小即可

而对于树边，发现它要比它参与构成的所有环中的非树边权值要小，因为非树边在其环中权职一定为最大的，若树边比它大，就不会在最小生成树中了

对于这两种操作，我们都可以用树剖来做，就是一个板子

注意：维护最小值的线段树维护的是边下放到它终点后的点权，记得在 (lca) 处不要多修改

Code

#include<bits/stdc++.h>
#define ri register signed
#define p(i) ++i
using namespace std;
namespace IO{
    char buf[1<<21],*p1=buf,*p2=buf;
    #define gc() p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++
    template<typename T>inline void read(T &x) {
        ri f=1;x=0;register char ch=gc();
        while(ch<'0'||ch>'9') {if (ch=='-') f=0;ch=gc();}
        while(ch>='0'&&ch<='9') {x=(x<<1)+(x<<3)+(ch^48);ch=gc();}
        x=f?x:-x;
    }
}
using IO::read;
namespace nanfeng{
    #define FI FILE *IN
    #define FO FILE *OUT
    template<typename T>inline T cmax(T x,T y) {return x>y?x:y;}
    template<typename T>inline T cmin(T x,T y) {return x>y?y:x;}
    static const int N=7e4+7,M=1e5+7,INF=2e9+7;
    int first[N],fa[N],W[N],hs[N],siz[N],dfn[N],top[N],bc[N],ans[M],dep[N],vis[M],tot,t=1,n,m,opt,num;
    struct edge{int v,nxt,w;}e[N<<1];
    struct edgei{int u,v,w,id;}G[M],AS[M];
    inline int cmp(edgei e1,edgei e2) {return e1.w<e2.w;}
    inline void add(int u,int v,int w) {
        e[t].v=v,e[t].w=w,e[t].nxt=first[u],first[u]=t++;
        e[t].v=u,e[t].w=w,e[t].nxt=first[v],first[v]=t++;
    }
    int find(int x) {return fa[x]==x?x:fa[x]=find(fa[x]);}
    inline void kruskal() {
        sort(G+1,G+m+1,cmp);
        for (ri i(1);i<=m;p(i)) {
            int u=G[i].u,v=G[i].v,w=G[i].w;
            if (find(u)==find(v)) continue;
            vis[G[i].id]=1;
            fa[find(u)]=find(v);
            add(u,v,w);
        }
    }
    struct Segmx{
        #define ls(x) (x<<1)
        #define rs(x) (x<<1|1)
        #define up(x) T[x].mx=cmax(T[ls(x)].mx,T[rs(x)].mx); 
        struct segmenttree{int mx;}T[N<<2];
        void build(int x,int l,int r) {
            if (l==r) return (void)(T[x].mx=W[bc[l]]);
            int mid(l+r>>1);
            build(ls(x),l,mid);
            build(rs(x),mid+1,r);
            up(x);
        }
        int querymx(int x,int l,int r,int lt,int rt) {
            if (l<=lt&&rt<=r) return T[x].mx;
            int mid(lt+rt>>1),res(0);
            if (l<=mid) res=cmax(res,querymx(ls(x),l,r,lt,mid));
            if (r>mid) res=cmax(res,querymx(rs(x),l,r,mid+1,rt));
            return res;
        }
    }Tx;
    struct Segmn{
        #define ls(x) (x<<1)
        #define rs(x) (x<<1|1)
        struct segmenttree{int mn,lz;segmenttree(){mn=INF;}}T[N<<2];
        inline void down(int x) {
            if (!T[x].lz) return;
            T[ls(x)].mn=cmin(T[x].mn,T[ls(x)].mn);
            T[rs(x)].mn=cmin(T[x].mn,T[rs(x)].mn);
            T[ls(x)].lz=T[rs(x)].lz=1;
            T[x].lz=0;
        } 
        void update(int x,int k,int l,int r,int lt,int rt) {
            if (l<=lt&&rt<=r) {
                T[x].mn=cmin(T[x].mn,k);
                return (void)(T[x].lz=1);
            }
            down(x);
            int mid(lt+rt>>1);
            if (l<=mid) update(ls(x),k,l,r,lt,mid);
            if (r>mid) update(rs(x),k,l,r,mid+1,rt);
        }
        int querymn(int x,int k,int l,int r) {
            if (l==r) return T[x].mn;
            int mid(l+r>>1);
            down(x);
            if (k<=mid) return querymn(ls(x),k,l,mid);
            else return querymn(rs(x),k,mid+1,r);
        }
    }Tn;
    void dfs1(int x,int f) {
        fa[x]=f;
        siz[x]=1;
        for (ri i(first[x]),v;i;i=e[i].nxt) {
            if ((v=e[i].v)==f) continue;
            W[v]=e[i].w,dep[v]=dep[x]+1;
            dfs1(v,x);
            siz[x]+=siz[v];
            if (siz[v]>siz[hs[x]]) hs[x]=v;
        }
    }
    void dfs2(int x,int tp) {
        bc[dfn[x]=p(tot)]=x;
        top[x]=tp;
        if (hs[x]) dfs2(hs[x],tp);
        for (ri i(first[x]),v;i;i=e[i].nxt) {
            if ((v=e[i].v)==fa[x]||v==hs[x]) continue;
            dfs2(v,v);
        }
    }
    inline int solve(int u,int v,int w) {
        ri res(0);
        while(top[u]!=top[v]) {
            if (dep[top[u]]<dep[top[v]]) swap(u,v);
            res=cmax(res,Tx.querymx(1,dfn[top[u]],dfn[u],1,n));
            Tn.update(1,w,dfn[top[u]],dfn[u],1,n);
            u=fa[top[u]];
        }
        if (dep[u]<dep[v]) swap(u,v);
        if (dfn[u]>dfn[v]) {
            res=cmax(res,Tx.querymx(1,dfn[v]+1,dfn[u],1,n));
            Tn.update(1,w,dfn[v]+1,dfn[u],1,n);
        }
        return res-1;
    }
    inline int main() {
        // FI=freopen("nanfeng.in","r",stdin);
        // FO=freopen("nanfeng.out","w",stdout);
        read(n),read(m),read(opt);
        for (ri i(1);i<=n;p(i)) fa[i]=i;
        for (ri i(1);i<=m;p(i)) 
            read(G[i].u),read(G[i].v),read(G[i].w),G[i].id=i,AS[i]=G[i];
        kruskal();
        dfs1(1,0),dfs2(1,1);
        Tx.build(1,1,n);
        for (ri i(1);i<=m;p(i)) {
            int u=AS[i].u,v=AS[i].v,w=AS[i].w;
            if (!dfn[u]) continue;
            if (vis[i]) continue;
            ans[i]=solve(u,v,w);
        }
        for (ri i(1);i<=m;p(i)) {
            int u=AS[i].u,v=AS[i].v,w=AS[i].w,lw=dep[u]<dep[v]?v:u;
            if (!dfn[u]) continue;
            if (vis[i]) ans[i]=Tn.querymn(1,dfn[lw],1,n)-1;
        }
        for (ri i(1);i<=m;p(i)) printf("%d ",ans[i]==INF-1?-1:ans[i]);
        return 0;
    }  
}
int main() {return nanfeng::main();}