图论：LCA-欧拉序 

  1 #include<cmath>
  2 #include<vector>
  3 #include<cstdio>
  4 #include<cstring>
  5 #include<iostream>
  6 #include<algorithm>
  7 using namespace std;
  8 
  9 vector<int > g[40010];
 10 int len,a[80020],dep[80020],pos[80020][17],dp[80020][17],vis[80020],cnt[80020];
 11 
 12 void dfs(int u,int fa,int deep)
 13 {
 14     a[++len]=u;
 15     dep[len]=deep+1;
 16     if(!vis[u])
 17     {
 18         cnt[u]=len;
 19         vis[u]=1;
 20     }
 21     int sz=g[u].size();
 22     for(int i=0; i<sz; i++)
 23     {
 24         if(g[u][i]!=fa)
 25         {
 26             dfs(g[u][i],u,deep+1);
 27             a[++len]=u;
 28             dep[len]=deep+1;
 29         }
 30     }
 31 }
 32 
 33 int main()
 34 {
 35     int t;
 36     scanf("%d",&t);
 37     while(t--)
 38     {
 39         int n,m;
 40         len=0;
 41         memset(a,0,sizeof(a));
 42         memset(dep,0,sizeof(dep));
 43         memset(pos,0,sizeof(pos));
 44         memset(dp,0,sizeof(dp));
 45         memset(vis,0,sizeof(vis));
 46         memset(cnt,0,sizeof(cnt));
 47         scanf("%d%d",&n,&m);
 48         for(int i=1; i<=n; i++)
 49         {
 50             g[i].clear();
 51         }
 52         for(int i=1; i<=n-1; i++)
 53         {
 54             int from,to;
 55             scanf("%d%d",&from,&to);
 56             g[from].push_back(to);
 57             g[to].push_back(from);
 58         }
 59         dfs(1,0,0);
 60         printf("%d\n",len);
 61         for(int i=1; i<=len; i++)
 62         {
 63             dp[i][0]=dep[i];
 64             pos[i][0]=i;
 65         }
 66         for(int j=1; j<=17; j++)
 67         {
 68             for(int i=1; i<=len; i++)
 69             {
 70                 if(i+(1<<(j-1))>=len)
 71                 {
 72                     break;
 73                 }
 74                 if(dp[i][j-1]>dp[i+(1<<(j-1))][j-1])
 75                 {
 76                     dp[i][j]=dp[i+(1<<(j-1))][j-1];
 77                     pos[i][j]=pos[i+(1<<(j-1))][j-1];
 78                 }
 79                 else
 80                 {
 81                     dp[i][j]=dp[i][j-1];
 82                     pos[i][j]=pos[i][j-1];
 83                 }
 84             }
 85         }
 86         for(int i=1; i<=m; i++)
 87         {
 88             int x,y;
 89             scanf("%d%d",&x,&y);
 90             int dx=cnt[x];
 91             int dy=cnt[y];
 92             if(dx>dy)
 93             {
 94                 swap(dx,dy);
 95                 swap(x,y);
 96             }
 97             int k=(int)(log((double)(dy-dx+1))/log(2.0));
 98             int p;
 99             if(dp[dx][k]>dp[dy-(1<<k)+1][k])
100             {
101                 p=pos[dy-(1<<k)+1][k];
102             }
103             else
104             {
105                 p=pos[dx][k];
106             }
107             printf("%d\n",a[p]);
108         }
109     }
110 
111 }

 

posted @ 2018-09-20 15:53  静听风吟。  阅读(359)  评论(0)    收藏  举报