luogu4185 [USACO18JAN]MooTube [并查集]

Posted 2022-04-30 lxyyyy

P4185 [USACO18JAN]MooTube 

并查集好合并不好拆开 可以考虑离线 先读入 从大到小排序 再依次合并

技巧：不好断开就倒着来合并 JSOI2008 P1197 也是该思想

#include<bits/stdc++.h>
using namespace std;
#define Max(x,y) (x)<(y)?(y):(x)
#define Min(x,y) (x)<(y)?(x):(y)
#define ll long long
#define rg register
const int N=300000+5,M=1000000+5,inf=0x3f3f3f3f,P=9999973;
int n,m,f[N],sz[N];
template <class t>void rd(t &x)
    x=0;int w=0;char ch=0;
    while(!isdigit(ch)) w|=ch==‘-‘,ch=getchar();
    while(isdigit(ch)) x=(x<<1)+(x<<3)+(ch^48),ch=getchar();
    x=w?-x:x;


int find(int x) return f[x]==x?x:f[x]=find(f[x]);
void merge(int x,int y)
    int fx=find(x),fy=find(y);
    if(fx==fy) return;
    sz[fx]+=sz[fy],f[fy]=fx;


struct edgeint u,v,w;e[N<<1];
struct nodeint k,v,pos,ans;ask[N];
bool cmp1(edge a,edge b)return a.w>b.w;
bool cmp2(node a,node b)return a.k>b.k;
bool cmp3(node a,node b)return a.pos<b.pos;

int main()
//    freopen("in.txt","r",stdin);
    rd(n),rd(m),f[n]=n,sz[n]=1;
    for(int i=1;i<n;++i) rd(e[i].u),rd(e[i].v),rd(e[i].w),f[i]=i,sz[i]=1;
    for(int i=1;i<=m;++i) rd(ask[i].k),rd(ask[i].v),ask[i].pos=i;
    sort(e+1,e+n,cmp1);
    sort(ask+1,ask+m+1,cmp2);
    for(int i=1,nxte=1;i<=m;++i)
        while(nxte<n&&e[nxte].w>=ask[i].k)
        merge(e[nxte].u,e[nxte].v),++nxte;
        ask[i].ans=sz[find(ask[i].v)]-1;
    
//    for(int i=1;i<=n;++i) printf("%d ",sz[i]);
    sort(ask+1,ask+m+1,cmp3);
    for(int i=1;i<=m;++i) printf("%d\n",ask[i].ans);
    return 0;