HDU - 2586 How far away ？(LCA)

题目大意：给出一张连通图，问两个点之间的距离

解题思路：LCA裸题

#include <cstdio>
#include <cstring>
#define N 40010
#define M 80010

struct Edge{
    int to, next, dis;
}E[M];

struct Question {
    int x, y;
}Q[N];

int n, m ,tot;
int head[N], dist[N], f[N], LCA[N];
bool vis[N];

void AddEdge(int u, int v, int dis) {
    E[tot].to = v; E[tot].dis = dis; E[tot].next = head[u]; head[u] = tot++;
    u = u ^ v; v = u ^ v; u = u ^ v;
    E[tot].to = v; E[tot].dis = dis; E[tot].next = head[u]; head[u] = tot++;
}

int find(int x) {
    return x == f[x] ? x : f[x] = find(f[x]);
}

void tarjan(int u) {
    vis[u] = true;
    f[u] = u; 

    for (int i = head[u]; i != -1; i = E[i].next) {
        int v = E[i].to;
        if (!vis[v]) {
            dist[v] = dist[u] + E[i].dis;
            tarjan(v);
            f[v] = u;
        }
    }
    for (int i = 0; i < m; i++) {
        if (u == Q[i].x && vis[Q[i].y])
            LCA[i] = find(Q[i].y);
        if (u == Q[i].y && vis[Q[i].x])
            LCA[i] = find(Q[i].x);
    }
}

void init() {
    memset(head, -1, sizeof(head));
    tot = 0;

    int u, v, d;
    scanf("%d%d", &n, &m);
    for (int i = 0; i < n - 1; i++) {
        scanf("%d%d%d", &u, &v, &d);
        AddEdge(u, v, d);
    }
    for (int i = 0; i < m; i++)  scanf("%d%d", &Q[i].x, &Q[i].y);

    memset(vis, 0, sizeof(vis));
}

void solve() {
    dist[1] = 0;
    tarjan(1);
    for (int i = 0; i < m; i++)
        printf("%d\n", dist[Q[i].x] + dist[Q[i].y] - 2 * dist[LCA[i]]);
}

int main() {
    int test;
    scanf("%d", &test);
    while (test--) {
        init();
        solve();
    }
    return 0;
}

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