88 lines
1.5 KiB
Plaintext
88 lines
1.5 KiB
Plaintext
#include "sylib.h"
|
|
int quick_read(){
|
|
int ch = getch(); int x = 0, f = 0;
|
|
while (ch < 48 || ch > 57){
|
|
if (ch == 45) f = 1;
|
|
ch = getch();
|
|
}
|
|
while (ch >= 48 && ch <=57){
|
|
x = x * 10 + ch - 48;
|
|
ch = getch();
|
|
}
|
|
if (f) return -x;
|
|
else return x;
|
|
}
|
|
#define maxn 10005
|
|
int n, m, f[maxn][20], dep[maxn];
|
|
int to[maxn], next[maxn], head[maxn], cnt = 0;
|
|
void add_edge(int from, int To){
|
|
to[cnt] = To;
|
|
next[cnt] = head[from];
|
|
head[from] = cnt;
|
|
cnt = cnt + 1;
|
|
f[To][0] = from;
|
|
}
|
|
void init(){
|
|
dep[0] = 0x3f3f3f3f;
|
|
int i = 1;
|
|
while (i <= n){
|
|
head[i] = -1;
|
|
i = i + 1;
|
|
}
|
|
}
|
|
void tree(int x, int d){
|
|
dep[x] = d;
|
|
int i = 0;
|
|
while (f[x][i]){
|
|
f[x][i + 1] = f[f[x][i]][i];
|
|
i = i + 1;
|
|
}
|
|
i = head[x];
|
|
while (i != -1){
|
|
int y = to[i];
|
|
tree(y, d + 1);
|
|
i = next[i];
|
|
}
|
|
}
|
|
int LCA(int x, int y){
|
|
if (dep[x] < dep[y]){
|
|
int t = x;
|
|
x = y;
|
|
y = t;
|
|
}
|
|
int i = 19;
|
|
while (dep[x] > dep[y]){
|
|
if (f[x][i] && dep[f[x][i]] >= dep[y])
|
|
x = f[x][i];
|
|
i = i - 1;
|
|
}
|
|
if (x == y) return x;
|
|
i = 19;
|
|
while (i >= 0){
|
|
if (f[x][i] != f[y][i]){
|
|
x = f[x][i];
|
|
y = f[y][i];
|
|
}
|
|
i = i - 1;
|
|
}
|
|
return f[x][0];
|
|
}
|
|
int main(){
|
|
n = quick_read(); m = quick_read();
|
|
init();
|
|
int i = 1;
|
|
while (i != n){
|
|
int x = quick_read(), y = quick_read();
|
|
add_edge(x, y);
|
|
i = i + 1;
|
|
}
|
|
tree(1, 1);
|
|
while (m){
|
|
int x = quick_read(), y = quick_read();
|
|
putint(LCA(x, y));
|
|
putch(10);
|
|
m = m - 1;
|
|
}
|
|
return 0;
|
|
}
|