树上路径交
计算两条路径的交点数量，直接载入任意 LCA 封装即可。
int intersection(int x, int y, int X, int Y) {vector<int> t = {lca(x, X), lca(x, Y), lca(y, X), lca(y, Y)};sort(t.begin(), t.end());int r = lca(x, y), R = lca(X, Y);if (dep[t[0]] < min(dep[r], dep[R]) || dep[t[2]] < max(dep[r], dep[R])) {return 0;}return 1 + clac(t[2], t[3]);
}