LCA 倍增算法模板
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1 #include <cstring> 2 #include <cstdio> 3 #include <cstdlib> 4 #include <algorithm> 5 #include <cmath> 6 #include <vector> 7 using namespace std; 8 const int N=10000+5; 9 vector <int> son[N]; 10 int T,n,depth[N],fa[N][20],in[N],a,b; 11 void dfs(int prev,int rt){ 12 depth[rt]=depth[prev]+1; 13 fa[rt][0]=prev; 14 for (int i=1;i<20;i++) 15 fa[rt][i]=fa[fa[rt][i-1]][i-1]; 16 for (int i=0;i<son[rt].size();i++) 17 dfs(rt,son[rt][i]); 18 } 19 int LCA(int x,int y){ 20 if (depth[x]<depth[y]) 21 swap(x,y); 22 for (int i=19;i>=0;i--) 23 if (depth[x]-(1<<i)>=depth[y]) 24 x=fa[x][i]; 25 if (x==y) 26 return x; 27 for (int i=19;i>=0;i--) 28 if (fa[x][i]!=fa[y][i]) 29 x=fa[x][i],y=fa[y][i]; 30 return fa[x][0]; 31 } 32 int main(){ 33 scanf("%d",&T); 34 while (T--){ 35 scanf("%d",&n); 36 for (int i=1;i<=n;i++) 37 son[i].clear(); 38 memset(in,0,sizeof in); 39 for (int i=1;i<n;i++){ 40 scanf("%d%d",&a,&b); 41 son[a].push_back(b); 42 in[b]++; 43 } 44 depth[0]=-1; 45 int rt=0; 46 for (int i=1;i<=n&&rt==0;i++) 47 if (in[i]==0) 48 rt=i; 49 dfs(0,rt); 50 scanf("%d%d",&a,&b); 51 printf("%d\n",LCA(a,b)); 52 } 53 return 0; 54 }
