Codeforces 150E Freezing with Style (树分治)

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#include <iostream>#include <algorithm>#include <cstdio>#include <cstring>using namespace std;#define N 100020#define M 200020#define inf 0x3f3f3f3fint fst[N], nxt[M], vv[M], cost[M], e;int n, m;int dep[N], fa[N], sz[N], cnt[N];int id[N], ord[N], dc;int pl, pr;int ans, ansu, ansv;int lstu, lstv;bool del[N];int mx[N], nmx[N];int who[N], nwho[N];int len1, len2;void init() {memset(fst, -1, sizeof fst);e = 0;}void add(int u, int v, int c) {vv[e] = v, nxt[e] = fst[u], cost[e] = c, fst[u] = e++;}void dfs(int u, int p, int chk, int c, int d) {dep[u] = d, cnt[u] = c;ord[++dc] = u;sz[u] = 1;fa[u] = p;for(int i = fst[u]; ~i; i = nxt[i]) {int v = vv[i];if(!del[v] && v != p) {dfs(v, u, chk, c + (cost[i] >= chk? 1: -1), d + 1);sz[u] += sz[v];}}}bool cmp(int u, int v) {return sz[u] < sz[v];}bool check() {static int q[N];int qh = 0, qt = 0;int L = len1, R = len1;for(int i = 0; i <= len2; ++i) {while(L >= 0 && L + i >= pl) {while(qh < qt && mx[L] >= mx[q[qt - 1]]) --qt;q[qt++] = L;L--;}while(qh < qt && q[qh] + i > pr) ++qh;if(qh < qt) {if(mx[q[qh]] + nmx[i] >= 0) {lstu = who[q[qh]];lstv = nwho[i];return true;}}}return false;}void solve(int rt) {dc = 0;dfs(rt, -1, -1, 0, 0);int mi = inf, sp;for(int i = 1; i <= dc; ++i) {int u = ord[i];int opt = sz[rt] - sz[u];for(int j = fst[u]; ~j; j = nxt[j]) {int v = vv[j];if(!del[v] && v != fa[u]) opt = max(opt, sz[v]);}if(opt < mi) mi = opt, sp = u;}rt = sp;del[rt] = 1;dc = 0;dfs(rt, -1, -1, 0, 0);static int ch[N];int nch = 0;for(int i = fst[rt]; ~i; i = nxt[i]) {int v = vv[i];if(!del[v]) {ch[++nch] = v;}}sort(ch + 1, ch + nch + 1, cmp);int l = -1, r = 1e9 + 1;while(l < r - 1) {int mid = (l + r) / 2;len1 = 0;mx[0] = 0, who[0] = rt;for(int i = fst[rt]; ~i; i = nxt[i]) {int v = vv[i];if(!del[v]) {cnt[v] = cost[i] >= mid? 1: -1;}}bool ok = false;for(int i = 1; i <= nch; ++i) {int u = ch[i];dc = 0;dfs(u, -1, mid, cnt[u], 1);len2 = 0;for(int j = 1; j <= dc; ++j) {len2 = max(len2, dep[ord[j]]);}for(int j = 0; j <= len2; ++j) nmx[j] = -inf;for(int j = 1; j <= dc; ++j) {int v = ord[j];if(cnt[v] > nmx[dep[v]]) {nmx[dep[v]] = cnt[v];nwho[dep[v]] = v;}}if(check()) {ok = true;break;}for(int i = 0; i <= len2; ++i) {if(i > len1 || nmx[i] > mx[i]) {mx[i] = nmx[i];who[i] = nwho[i];}}len1 = max(len1, len2);}if(ok) {l = mid;}else r = mid;}if(l >= ans) ans = l, ansu = lstu, ansv = lstv;for(int i = fst[rt]; ~i; i = nxt[i]) {int v = vv[i];if(!del[v]) solve(v);}}int main() {scanf("%d%d%d", &n, &pl, &pr);init();for(int i = 1; i < n; ++i) {int u, v, c;scanf("%d%d%d", &u, &v, &c);add(u, v, c);add(v, u, c);}solve(1);printf("%d %d\n", ansu, ansv);return 0;}
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