sysy-data/hidden_functional_c/sy/13_LCA.sy

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2024-06-02 22:04:54 +08:00
#include "sylib.h"
2024-06-14 13:25:10 +08:00
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;
}