Dfs order Qauqaut of the game
Two \ (n \) node of the tree, not the same, ask how many points \ ((u, v) \ ) in both trees are met path \ (v \) in \ (u \) subtree
\ (N \ 10 ^ 5 \)
violence:
\ (n ^ 2 \) violence enumerated by points \ (DFS \) sequence \ (O (1) \) determines a non-satisfied condition,Or Euler sequence \ (O (1) \) seeking lca
Correct answer:
Xianpao first tree, which obtains \ (DFS \) sequence, node record \ (I \) a \ (DFS \) sequence starting and ending position.
Then ran the second tree, maintaining a subscript \ (dfs \) Fenwick tree sequence, the first pass to each node \ (i \) , we count the current node in \ (dfs \) before the sequence ( is met on the first node tree \ (I \) in \ (J \) in the subtree), and in that the current has traversed a second tree node (i.e., a second tree node satisfies \ (I \) in \ (J \) subtree) number, added to the answer. This process is equivalent statistics for each \ ((u, v) \ ) in the \ (v \) .
Look at the specific code to achieve it.
#include <cstdio>
#define MAXN 100001
using namespace std;
inline int read(){
char ch=getchar();int s=0;
while(ch<'0'||ch>'9') ch=getchar();
while(ch>='0'&&ch<='9') s=s*10+(ch^'0'), ch=getchar();
return s;
}
int n;
int tre[MAXN];
void add(int x, int val){
while(x<=n)
tre[x]+=val,x+=x&(-x);
}
int get_sum(int x){
int res=0;
while(x>0)
res+=tre[x],x-=x&(-x);
return res;
}
int dfn[MAXN],dfn_out[MAXN],cnt;
int ans[MAXN];
namespace tre1 {
int head[MAXN],nxt[MAXN*2],vv[MAXN*2],tot;
inline void add_edge(int u, int v){
vv[++tot]=v;
nxt[tot]=head[u];
head[u]=tot;
}
void dfs(int u, int fa){
dfn[u]=++cnt;
for(int i=head[u];i;i=nxt[i]){
int v=vv[i];
if(v==fa) continue;
dfs(v, u);
}
dfn_out[u]=cnt;
}
}
namespace tre2 {
int head[MAXN],nxt[MAXN*2],vv[MAXN*2],tot;
inline void add_edge(int u, int v){
vv[++tot]=v;
nxt[tot]=head[u];
head[u]=tot;
}
void solve(int u, int fa){
ans[u]=get_sum(dfn[u]-1);
add(dfn[u], 1);
add(dfn_out[u], -1);
for(int i=head[u];i;i=nxt[i]){
int v=vv[i];
if(v==fa) continue;
solve(v, u);
}
add(dfn[u], -1);
add(dfn_out[u], 1);
}
}
int main(){
//freopen("climb.in", "r", stdin);
//freopen("climb.out", "w", stdout);
n=read();
for(int i=1;i<n;++i){
int u=read(),v=read();
tre1::add_edge(u, v);
tre1::add_edge(v, u);
}
for(int i=1;i<n;++i){
int u=read(),v=read();
tre2::add_edge(u, v);
tre2::add_edge(v, u);
}
tre1::dfs(1, 1);
tre2::solve(1, 1);
long long sum=0;
for(int i=1;i<=n;++i) sum+=ans[i];
printf("%lld", sum);
return 0;
}