NOIP Day1 T3 货车运输

  1 #include<cstdio>
  2 #include<iostream>
  3 #include<cmath>
  4 #include<queue>
  5 #include<stack>
  6 #include<iomanip>
  7 #include<string>
  8 #include<cstring>
  9 #include<vector>
 10 #include<bitset>
 11 #include<algorithm>
 12 using namespace std;
 13 struct data
 14 {
 15     int x,y,z;
 16 };
 17     data tr[50005];
 18 struct node
 19 {
 20     int l,w;
 21 };
 22     node tt;
 23 vector <node> te[10005];
 24 int n,m,a,b,c,q,k=1;
 25 int fa[10005],dep[10005],dis[10005][25],f[10005][25];
 26 bool vis[10005];
 27 bool comp(data a,data b)
 28 {
 29     if (a.z>=b.z)  return true;
 30     return false;
 31 }
 32 int find (int x){
 33     if (fa[x]==x)  return x;
 34     else {
 35         fa[x]=find(fa[x]);
 36         return fa[x];
 37     }
 38 }
 39 void kruskal(){
 40     for (int i=1;i<=m;i++)
 41     {
 42         int r1=find(tr[i].x);
 43         int r2=find(tr[i].y);
 44         if (r2!=r1){
 45             fa[r2]=r1;//here
 46             tt.l=tr[i].y;tt.w=tr[i].z;
 47             te[tr[i].x].push_back(tt);
 48             tt.l=tr[i].x;tt.w=tr[i].z;
 49             te[tr[i].y].push_back(tt);
 50         }
 51     }
 52 }
 53 void dfs(int x)
 54 {
 55     vis[x]=true;
 56     for (int i=0;i<te[x].size();i++)
 57         if (!vis[te[x][i].l])
 58         {
 59             dep[te[x][i].l]=dep[x]+1;
 60             dis[te[x][i].l][0]=te[x][i].w;
 61             f[te[x][i].l][0]=x;
 62             dfs(te[x][i].l);
 63         }
 64 }
 65 void init()
 66 {
 67     for (int j=1;(1<<j)<=n;j++)
 68         for(int i=1;i<=n;i++)
 69         {
 70             f[i][j]=f[f[i][j-1]][j-1];
 71             dis[i][j]=min(dis[f[i][j-1]][j-1],dis[i][j-1]);
 72         }
 73 }
 74 int lca(int x,int y)
 75 {
 76     int sm=10000000;
 77     if (dep[x]>dep[y])  swap(x,y);
 78     int h=dep[y]-dep[x];
 79     for (int i=0;(1<<i)<=h;i++)
 80         if ((1<<i)&h)
 81         {
 82             sm=min(sm,dis[y][i]);
 83             y=f[y][i];
 84         }
 85             
 86     if (x!=y)
 87     {
 88         for (int i=(int)log2(n);i>=0;i--)
 89             if (f[x][i]!=f[y][i])
 90             {
 91                 sm=min(sm,min(dis[x][i],dis[y][i]));
 92                 x=f[x][i];y=f[y][i];
 93             }
 94         sm=min(sm,min(dis[x][0],dis[y][0]));
 95         x=f[x][0];
 96     }
 97     return sm;
 98 }
 99 int main()
100 {
101     freopen ("truck.in","r",stdin);
102     //freopen ("truck.out","w",stdout);
103     scanf ("%d%d",&n,&m);
104     for (int i=1;i<=n;i++)  fa[i]=i;
105     for (int i=1;i<=m;i++)
106     {
107         scanf ("%d%d%d",&a,&b,&c);
108         tr[i].x=a;
109         tr[i].y=b;
110         tr[i].z=c;
111     }
112     sort(tr+1,tr+m+1,comp);
113     kruskal();
114     dep[1]=1;
115     dfs(1);
116     init();
117     scanf ("%d",&q);
118     for (int i=1;i<=q;i++)
119     {
120         scanf ("%d%d",&a,&b);
121         if (find(a)!=find(b))  printf ("-1\n");
122         else
123         {
124             int s=lca(a,b);
125             printf ("%d\n",s);
126         }
127     }
128     return 0;
129 }