点的距离

题目描述

思路

lca 模板题

代码

#include <cstdio>
#include <algorithm>
using namespace std;

const int MAX = 1e5 + 5;
int n, m;
int head[MAX], ver[MAX << 1], nxt[MAX << 1], ht;
int dep[MAX], fa[MAX][22];
void add(int x, int y) {
	nxt[++ht] = head[x], head[x] = ht, ver[ht] = y;
}
inline int read() {
	int s = 0;
	char ch = getchar();
	while (ch < '0' || ch > '9') ch = getchar();
	while (ch >= '0' && ch <= '9') s = s * 10 + ch - '0', ch = getchar();
	return s;
}
void dfs(int x, int u) {
	fa[x][0] = u;
	dep[x] = dep[u] + 1;
	for (int i = 1; i <= 20; ++i) fa[x][i] = fa[fa[x][i - 1]][i - 1];
	for (int i = head[x], j; i; i = nxt[i]) {
		j = ver[i];
		if (j == u) continue;
		dfs(j, x);
	}
}
int lca(int x, int y) {
	if (dep[x] < dep[y]) swap(x, y);
	for (int i = 20; i >= 0; --i) {
		if (dep[fa[x][i]] >= dep[y]) x = fa[x][i];
		if (x == y) return x;
	}
	for (int i = 20; i >= 0; --i) {
		if (fa[x][i] != fa[y][i]) {
			x = fa[x][i];
			y = fa[y][i];
		}
	}
	return fa[x][0];
}
int dist(int a, int b) {
	return dep[a] + dep[b] - (dep[lca(a, b)] << 1);
}
int main() {
	n = read();
	for (int i = 1, a, b; i < n; ++i) {
		a = read(), b = read();
		add(a, b), add(b, a);
	}
	dfs(1, 0);
	m = read();
	for (int i = 1, a, b; i <= m; ++i) {
		a = read(), b = read();
		printf("%d
", dist(a, b));
	}
	return 0;
}