noip2013truck树上路径倍增

#include <iostream>#include <cstdio>#include <cstring>#include <cstdlib>#include <algorithm>using namespace std;#define INF 0x7fffffffint n,m,x,y,z,l,s,u,v,q;bool vis[10010];struct point{int x,y,z;}a[50010];struct node{int y,z,next;}edge[500010];int father[50010],deep[50010],head[50010];int f[50010][20],g[50010][20];int cmp(point a,point b){return a.z>b.z;}int find(int x){if (father[x]!=x)father[x]=find(father[x]);return father[x];}void add(int x,int y,int z){l++;edge[l].y=y;edge[l].z=z;edge[l].next=head[x];head[x]=l;}void dfs(int x){    vis[x]=1;for (int i=head[x];i!=0;i=edge[i].next){if (vis[edge[i].y]==0){deep[edge[i].y]=deep[x]+1;f[edge[i].y][0]=x;g[edge[i].y][0]=edge[i].z;dfs(edge[i].y);}}}void dp(){for (int j=1;j<=15;j++)for (int i=1;i<=n;i++){f[i][j]=f[f[i][j-1]][j-1];g[i][j]=min(g[i][j-1],g[f[i][j-1]][j-1]);}}int lca(int x,int y){int t,ans=INF;if (find(x)!=find(y)) return -1;if (deep[x]>deep[y]){t=x;x=y;y=t;}for (int i=15;i>=0;i--)  if (deep[f[y][i]]>=deep[x])  {  ans=min(ans,g[y][i]);  y=f[y][i];  }    if (x==y) return ans;    for (int i=15;i>=0;i--)//这里算到0！！，因为跳到的地方是父节点不相同的地方，最后在往上跳一个  if (f[x][i]!=f[y][i]) {    ans=min(ans,g[x][i]); ans=min(ans,g[y][i]);x=f[x][i];y=f[y][i]; }    ans=min(ans,g[x][0]);ans=min(ans,g[y][0]);return ans;}int main(){    freopen("truck.in","r",stdin);    freopen("truck.out","w",stdout);scanf("%d%d", &n, &m);for (int i=1;i<=m;i++)        scanf("%d%d%d",&a[i].x, &a[i].y, &a[i].z);sort(a+1,a+m+1,cmp);for (int i=1;i<=n;i++) father[i]=i;s=0;memset(head,0,sizeof(head));for (int i=1;i<=m;i++){    u=find(a[i].x);v=find(a[i].y);if (u!=v){s++;father[u]=father[v];add(a[i].x,a[i].y,a[i].z);add(a[i].y,a[i].x,a[i].z);}if (s==n-1) break;}memset(vis,0,sizeof(vis));memset(f,0,sizeof(f));    memset(g,0x3f,sizeof(g));for (int i=1;i<=n;i++){if (!vis[i]){deep[i]=1;dfs(i);}}dp();scanf("%d", &q);while (q--){        scanf("%d%d", &x, &y);printf("%d\n", lca(x,y));}    fclose(stdin);    fclose(stdout);return 0;}