/** LCA在線算法(倍增法) */ const int MAXN = 10010; const int DEG = 20;struct Edge {int to, next; } edge[MAXN * 2];int head[MAXN], tot; void addedge(int u, int v) {edge[tot].to = v;edge[tot].next = head[u];head[u] = tot++; }void init() {tot = 0;memset(head, -1, sizeof(head)); }int fa[MAXN][DEG]; // fa[i][j]表示結點i的第2^j個祖先 int deg[MAXN]; // 深度數組void BFS(int root) {queue<int>que;deg[root] = 0;fa[root][0] = root;que.push(root);while (!que.empty()){int tmp = que.front();que.pop();for (int i = 1; i < DEG; i++){fa[tmp][i] = fa[fa[tmp][i - 1]][i - 1];}for (int i = head[tmp]; i != -1; i = edge[i].next){int v = edge[i].to;if (v == fa[tmp][0]){continue;}deg[v] = deg[tmp] + 1;fa[v][0] = tmp;que.push(v);}} }int LCA(int u, int v) {if (deg[u] > deg[v]){swap(u, v);}int hu = deg[u], hv = deg[v];int tu = u, tv = v;for (int det = hv-hu, i = 0; det ; det >>= 1, i++){if (det & 1){tv = fa[tv][i];}}if (tu == tv){return tu;}for (int i = DEG - 1; i >= 0; i--){if (fa[tu][i] == fa[tv][i]){continue;}tu = fa[tu][i];tv = fa[tv][i];}return fa[tu][0]; }bool flag[MAXN];int main() {int T;int n;int u, v;scanf("%d", &T);while(T--){scanf("%d", &n);init();memset(flag, false, sizeof(flag));for (int i = 1; i < n; i++){scanf("%d%d", &u, &v);addedge(u, v);addedge(v, u);flag[v] = true;}int root;for (int i = 1; i <= n; i++){if (!flag[i]){root = i;break;}}BFS(root);scanf("%d%d", &u, &v);printf("%d\n", LCA(u, v));}return 0; }

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