[USACO18JAN] MooTube (并查集 -> 维护连通性)

 1 #include <bits/stdc++.h>
 2 #define N 200100
 3 #define inf 0x3f3f3f3f
 4 using namespace std;
 5 
 6 int n,q,cnt;
 7 int fa[N],f[N];
 8 struct EDGE{
 9     int x,y,w;
10 }edge[N];
11 struct QUES{
12     int k,v,id,ans;
13 }ques[N];
14 
15 int cmp1(EDGE s1,EDGE s2) {return s1.w>s2.w;}
16 int cmp2(QUES s1,QUES s2) {return s1.k>s2.k;}
17 int cmp3(QUES s1,QUES s2) {return s1.id<s2.id;}
18 void edge_add(int x,int y,int z)
19 {
20     cnt++;
21     edge[cnt].x=x;
22     edge[cnt].y=y;
23     edge[cnt].w=z;
24 }
25 int find_fa(int x)
26 {
27     int fx=x;
28     while(fx!=fa[fx]) {fx=fa[fx];}
29     while(fa[x]!=fx)
30     {
31         int pr=fa[x];
32         f[pr]-=f[x];
33         fa[x]=fx;
34         x=pr;
35     }
36     return fx;
37 }
38 void comb(int x,int y)
39 {
40     int fx=find_fa(x);
41     int fy=find_fa(y);
42     fa[fy]=fx;
43     f[fx]+=f[fy];
44 }
45 
46 int main()
47 {
48     scanf("%d%d",&n,&q);
49     for(int i=1;i<n;i++)
50     {
51         int x,y,z;
52         scanf("%d%d%d",&x,&y,&z);
53         edge_add(x,y,z);
54     }
55     sort(edge+1,edge+n,cmp1);
56     for(int i=1;i<=q;i++)
57     {
58         int x,y;
59         scanf("%d%d",&x,&y);
60         ques[i].k=x;
61         ques[i].v=y;
62         ques[i].id=i;
63     }
64     sort(ques+1,ques+q+1,cmp2);
65     for(int i=1;i<=n;i++) 
66     {
67         fa[i]=i;
68         f[i]=1;
69     }
70     int j=1;
71     for(int i=1;i<=q;i++)
72     {
73         while(edge[j].w>=ques[i].k)
74         {
75             comb(edge[j].x,edge[j].y);
76             j++;
77         }
78         int fv=find_fa(ques[i].v);
79         ques[i].ans=f[fv]-1;
80     }
81     sort(ques+1,ques+q+1,cmp3);
82     for(int i=1;i<=q;i++)
83     {
84         printf("%d\n",ques[i].ans);
85     }
86     return 0;
87 }