LCA模板 Tarjan

#include<iostream>#include<algorithm>#include<cstdio>#include<cstring>#include<string.h>using namespace std;const int maxn = 50005;int n, m, num,qnum, ans;int head[maxn], qhead[maxn], fa[maxn], dis[maxn], f[maxn][20], a[maxn][3];bool vis[maxn];struct node {int next, to, dist;}e[maxn];struct qnode{int next, to, k;}q[maxn<<1];void add(int from,int to,int dist){e[++num].next = head[from];e[num].to = to;e[num].dist = dist;head[from] = num;}void qadd(int from, int to, int k){q[++qnum].next = qhead[from];q[num].to = to;q[num].k = k;qhead[from] = qnum;}int find(int x){if (x == fa[x])return fa[x];return fa[x] = fa[fa[x]];}void merge(int x, int y){int fx = find(x);int fy = find(y);fa[fx] = fy;}void tarjan(int x){vis[x] = true;for (int i = qhead[x]; i; i = q[i].next) {int to = q[i].to;int k = q[i].k;if (vis[to])a[k][2] = find(to);}for (int i = head[x]; i; i = e[i].next) {int to = e[i].to;if (!vis[to]) {dis[to] = dis[x] + e[i].dist;tarjan(to);merge(to, x);}}}int main(){cin >> n;for (int i = 0; i < n; i++)fa[i] = i;for (int i = 1; i < n; i++) {int u, v, d;cin >> u >> v >> d;add(u, v, d);add(v, u, d);}cin >> m;for (int i = 1; i <= m; i++) {cin >> a[i][0] >> a[i][1];qadd(a[i][0], a[i][1], i);qadd(a[i][1], a[i][0], i);}tarjan(0);for (int i = 1; i <= m; i++) {cout << dis[a[i][0]] + dis[a[i][1]] - 2 * dis[a[i][2]];}return 0;}