树论大封装（直径+重心+中心）
struct Tree {int n;vector<vector<pair<int, int>>> e;vector<int> dep, parent, maxdep, d1, d2, s1, s2, up;Tree(int n) {this->n = n;e.resize(n + 1);dep.resize(n + 1);parent.resize(n + 1);maxdep.resize(n + 1);d1.resize(n + 1);d2.resize(n + 1);s1.resize(n + 1);s2.resize(n + 1);up.resize(n + 1);}void add(int u, int v, int w) {e[u].push_back({w, v});e[v].push_back({w, u});}void dfs(int u, int fa) {maxdep[u] = dep[u];for (auto [w, v] : e[u]) {if (v == fa) continue;dep[v] = dep[u] + 1;parent[v] = u;dfs(v, u);maxdep[u] = max(maxdep[u], maxdep[v]);}}void dfs1(int u, int fa) {for (auto [w, v] : e[u]) {if (v == fa) continue;dfs1(v, u);int x = d1[v] + w;if (x > d1[u]) {d2[u] = d1[u], s2[u] = s1[u];d1[u] = x, s1[u] = v;} else if (x > d2[u]) {d2[u] = x, s2[u] = v;}}}void dfs2(int u, int fa) {for (auto [w, v] : e[u]) {if (v == fa) continue;if (s1[u] == v) {up[v] = max(up[u], d2[u]) + w;} else {up[v] = max(up[u], d1[u]) + w;}dfs2(v, u);}}int radius, center, diam;void getCenter() {center = 1; //中心for (int i = 1; i <= n; i++) {if (max(d1[i], up[i]) < max(d1[center], up[center])) {center = i;}}radius = max(d1[center], up[center]); //距离最远点的距离的最小值diam = d1[center] + up[center] + 1; //直径}int rem; //删除重心后剩余连通块体积的最小值int cog; //重心vector<bool> vis;void getCog() {vis.resize(n);rem = INT_MAX;cog = 1;dfsCog(1);}int dfsCog(int u) {vis[u] = true;int s = 1, res = 0;for (auto [w, v] : e[u]) {if (vis[v]) continue;int t = dfsCog(v);res = max(res, t);s += t;}res = max(res, n - s);if (res < rem) {rem = res;cog = u;}return s;}
};