感觉码力严重下降~
#include <bits/stdc++.h>
#define N 400006
#define inf 1000000000
#define setIO(s) freopen(s".in","r",stdin)
using namespace std;
multiset<int>S;
multiset<int>::iterator it;
struct Edge
{int u,v,c; Edge(int u=0,int v=0,int c=0):u(u),v(v),c(c){}
}e[N];
bool cmp(Edge a,Edge b)
{return a.c<b.c;
}
struct Union
{int p[N]; void init() {for(int i=1;i<N;++i) p[i]=i; } int find(int x) {return p[x]==x?x:p[x]=find(p[x]); }int merge(int x,int y) {x=find(x),y=find(y); if(x!=y) {p[x]=y; return 1; } return 0; }
}ufs;
struct Link_Cut_Tree
{ #define lson t[x].ch[0] #define rson t[x].ch[1] int sta[N]; struct Node { int ch[2],f,min,id,val,rev; }t[N]; int isrt(int x) {return !(t[t[x].f].ch[0]==x||t[t[x].f].ch[1]==x); }int get(int x) {return t[t[x].f].ch[1]==x; } void pushup(int x) { t[x].min=t[x].val, t[x].id=x; if(lson && t[lson].min<t[x].min) t[x].min=t[lson].min,t[x].id=t[lson].id; if(rson && t[rson].min<t[x].min) t[x].min=t[rson].min,t[x].id=t[rson].id; } void mark(int x) { if(x) t[x].rev^=1,swap(lson,rson); }void pushdown(int x) { if(t[x].rev) {if(lson) mark(lson); if(rson) mark(rson); t[x].rev=0; }}void rotate(int x) {int old=t[x].f,fold=t[old].f,which=get(x); if(!isrt(old)) t[fold].ch[t[fold].ch[1]==old]=x; t[old].ch[which]=t[x].ch[which^1], t[t[old].ch[which]].f=old; t[x].ch[which^1]=old,t[old].f=x,t[x].f=fold; pushup(old),pushup(x); } void splay(int x) {int v=0,u=x,fa; for(sta[++v]=u;!isrt(u);u=t[u].f) sta[++v]=t[u].f; for(;v;--v) pushdown(sta[v]); for(u=t[u].f;(fa=t[x].f)!=u;rotate(x)) if(t[fa].f!=u) rotate(get(fa)==get(x)?fa:x); }void Access(int x) {for(int y=0;x;y=x,x=t[x].f) splay(x),rson=y,pushup(x); }void makeroot(int x) {Access(x),splay(x),mark(x); } void link(int x,int y) {makeroot(x),t[x].f=y; } void cut(int x,int y) {makeroot(x),Access(y),splay(y); t[t[y].ch[0]].f=0; t[y].ch[0]=0; pushup(y); } void split(int x,int y) {makeroot(x),Access(y),splay(y); }#undef lson #undef rson
}op;
int main()
{ int i,j,n,m,ans=inf; // setIO("input"); scanf("%d%d",&n,&m); for(i=1;i<=m;++i) scanf("%d%d%d",&e[i].u,&e[i].v,&e[i].c); sort(e+1,e+1+m,cmp); ufs.init(); for(i=1;i<=n;++i) op.t[i].val=inf; for(i=1;i<=m;++i) { int x=e[i].u,y=e[i].v,c=e[i].c,_new=i+n; if(x==y) continue; if(ufs.merge(x,y)) { op.t[_new].val=c; op.link(x,_new); op.link(_new,y); S.insert(c); } else{op.split(x,y); if(op.t[y].min<c) { S.erase(S.find(op.t[y].min)); S.insert(c); int kk=op.t[y].id; int xx=e[kk-n].u; int yy=e[kk-n].v; op.cut(xx,kk); op.cut(yy,kk); op.t[_new].val=c; op.link(x,_new); op.link(_new,y); }} if(S.size()>=n-1) {it=S.end(); it--; ans=min(ans,*(it)-*(S.begin())); }} printf("%d\n",ans); return 0;
}
