【倍增法】
1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<cstdlib> 5 #include<ctime> 6 #include<cmath> 7 #include<algorithm> 8 using namespace std; 9 #define MAXN 100010 10 struct node{int y,next;}e[MAXN*2]; 11 int n,m,len,Link[MAXN],deep[MAXN],f[MAXN],anc[MAXN][25]; 12 inline int read() 13 { 14 int x=0,f=1; char ch=getchar(); 15 while(!isdigit(ch)) {if(ch=='-') f=-1; ch=getchar();} 16 while(isdigit(ch)) {x=x*10+ch-'0'; ch=getchar();} 17 return x*f; 18 } 19 void insert(int x,int y) {e[++len].next=Link[x];Link[x]=len;e[len].y=y;} 20 void dfs(int x,int fa) 21 { 22 anc[x][0]=f[x]; 23 for(int i=1;i<=20;i++) anc[x][i]=anc[anc[x][i-1]][i-1]; 24 for(int i=Link[x];i;i=e[i].next) 25 if(e[i].y!=fa) 26 { 27 f[e[i].y]=x; 28 deep[e[i].y]=deep[x]+1; 29 dfs(e[i].y,x); 30 } 31 } 32 int lca(int x,int y) 33 { 34 if(deep[x]<deep[y]) swap(x,y); 35 for(int i=20;i>=0;i--) 36 if(deep[anc[x][i]]>=deep[y]) x=anc[x][i]; 37 if(x==y) return x; 38 for(int i=20;i>=0;i--) 39 if(anc[x][i]!=anc[y][i]) x=anc[x][i],y=anc[y][i]; 40 return f[x]; 41 } 42 int main() 43 { 44 //freopen("cin.in","r",stdin); 45 //freopen("cout.out","w",stdout); 46 n=read(); m=read(); 47 for(int i=1;i<n;i++) {int x=read(),y=read(); insert(x,y); insert(y,x);} 48 deep[1]=1; dfs(1,0); 49 for(int i=1;i<=m;i++) 50 { 51 int x=read(),y=read(); 52 printf("%d ",lca(x,y)); 53 } 54 return 0; 55 }
【树剖法】
1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<cstdlib> 5 #include<cmath> 6 #include<algorithm> 7 #include<ctime> 8 using namespace std; 9 struct node{int y,next;}e[201000]; 10 int n,m,len,z,a[201000],dep[201000],f[201000],top[201000],son[201000],size[201000]; 11 inline int read() 12 { 13 int x=0,f=1; char ch=getchar(); 14 while(!isdigit(ch)) {if(ch=='-') f=-1; ch=getchar();} 15 while(isdigit(ch)) {x=x*10+ch-'0'; ch=getchar();} 16 return x*f; 17 } 18 void insert(int xx,int yy) 19 { 20 e[++len].next=a[xx]; 21 a[xx]=len; 22 e[len].y=yy; 23 } 24 void dfs1(int x) 25 { 26 dep[x]=dep[f[x]]+1; size[x]=1; 27 for(int i=a[x];i;i=e[i].next) 28 { 29 if(e[i].y!=f[x]&&!f[e[i].y]) 30 { 31 f[e[i].y]=x; 32 dfs1(e[i].y); 33 size[x]+=size[e[i].y]; 34 if(size[son[x]]<size[e[i].y]) son[x]=e[i].y; 35 } 36 } 37 } 38 void dfs2(int x) 39 { 40 if(x==son[f[x]]) top[x]=top[f[x]]; 41 else top[x]=x; 42 for(int i=a[x];i;i=e[i].next) 43 if(f[e[i].y]==x) dfs2(e[i].y); 44 } 45 int ask(int xx,int yy) 46 { 47 while(top[xx]!=top[yy]) 48 { 49 if(dep[top[xx]]>dep[top[yy]]) xx=f[top[xx]]; 50 else yy=f[top[yy]]; 51 } 52 if(dep[xx]<dep[yy]) return xx; 53 else return yy; 54 } 55 int main() 56 { 57 n=read(); m=read(); 58 for(int i=1;i<n;i++) 59 { 60 int xx=read(),yy=read(); 61 insert(xx,yy); 62 insert(yy,xx); 63 } 64 dfs1(1); 65 dfs2(1); 66 for(int i=1;i<=m;i++) 67 { 68 int xx=read(),yy=read(); 69 printf("%d ",ask(xx,yy)); 70 } 71 return 0; 72 }