| # | 제출 시각 | 아이디 | 문제 | 언어 | 결과 | 실행 시간 | 메모리 |
|---|---|---|---|---|---|---|---|
| 445189 | Tizariox | 경주 (Race) (IOI11_race) | C++17 | 0 ms | 0 KiB |
이 제출은 이전 버전의 oj.uz에서 채점하였습니다. 현재는 제출 당시와는 다른 서버에서 채점을 하기 때문에, 다시 제출하면 결과가 달라질 수도 있습니다.
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define MOD 1000000007
#define nl "\n"
#define pb push_back
int n, k;
vector<pii> adjLists[200000];
int par[200000];
int subTreeSize[200000];
bool vis[200000];
int dist[200000];
int anc[200000][19];
void findAncestors() {
for (int i = 0; i < n; i++) {
if (dist[i] != 0) {
anc[i][0] = par[i];
}
}
for (int j = 1; j <= 18; j++) {
for (int i = 0; i < n; i++) {
if (dist[i] != 0) {
anc[i][j] = anc[anc[i][j - 1]][j - 1];
}
}
}
}
void treeDfs2(int node, int prevNode) {
for (int i = 0; i < adjLists[node].size(); i++) {
if (adjLists[node][i].first != prevNode) {
pii child = adjLists[node][i];
par[child.first] = node;
dist[child.first] = dist[node] + 1;
treeDfs2(child.first, node);
}
}
}
int lca(int a, int b) {
if (dist[a] > dist[b]) { // swap if a is further
return lca(b, a);
}
if (dist[a] < dist[b]) { // find ancestor of b that's the same depth as a
for (int k = 18; dist[b] != dist[a]; k--) {
while (dist[b] - (1 << k) >= dist[a]) {
b = anc[b][k];
}
}
}
for (int k = 18; k > 0; k--) {
while (anc[a][k] != anc[b][k]) {
a = anc[a][k];
b = anc[b][k];
}
}
while (a != b) {
a = par[a];
b = par[b];
}
return a;
}
int distance(int a, int b) {
int ancestor = lca(a, b);
return dist[a] + dist[b] - 2 * dist[ancestor];
}
void calcSubtrees(int node) {
for (pii i : adjLists[node]) {
if (i.first != par[node]) {
calcSubtrees(i.first);
subTreeSize[node] += subTreeSize[i.first];
}
}
}
unordered_set<int> visited;
int findCentroid(int node) {
// we don't need to worry about the parent and its subtrees because we
// already know it's not a centroid
visited.insert(node);
for (pii i : adjLists[node]) {
if (visited.count(i.first) == 0) {
if (subTreeSize[i.first] * 2 > n) {
return findCentroid(i.first);
} else {
return node;
}
}
}
return -1;
}
int minOverallPath = 1e9;
int minPath;
void treeDfs1(int node, int path, int root) {
if (path == k) {
minPath = min(minPath, distance(node, root));
return;
}
visited.insert(node);
for (int i = 0; i < adjLists[node].size(); i++) {
pii child = adjLists[node][i];
if (visited.count(child.first) > 0 || vis[child.first]) {
continue;
}
treeDfs1(child.first, path + child.second, root);
}
}
unordered_map<int, pii> nodeDists;
queue<pair<int, pii>> nodeDistsQueue;
void treeDfs3(int node, int path, int root) {
if (nodeDists.find(path) != nodeDists.end()) {
if (distance(node, root) < (*nodeDists.find(path)).second.second) {
nodeDists[path] = pii(distance(node, root), node);
}
} else {
nodeDistsQueue.push(make_pair(path, pii(distance(node, root), node)));
if (nodeDists.find(k - path) != nodeDists.end()) {
minPath = min(minPath, distance(node, root) + distance((*nodeDists.find(k - path)).second.second, root));
}
}
visited.insert(node);
for (int i = 0; i < adjLists[node].size(); i++) {
pii child = adjLists[node][i];
if (visited.count(child.first) > 0 || vis[child.first]) {
continue;
}
treeDfs3(child.first, path + child.second, root);
}
}
void decomp(int node) {
int centroid = findCentroid(node);
vis[centroid] = true;
minPath = 1e9;
treeDfs1(centroid, 0, centroid);
visited.clear();
for (pii i : adjLists[centroid]) {
if (vis[i.first]) {
continue;
}
treeDfs3(i.first, i.second, centroid);
visited.clear();
while (!nodeDistsQueue.empty()) {
nodeDists.insert(nodeDistsQueue.front());
nodeDistsQueue.pop();
}
}
nodeDists.clear();
minOverallPath = min(minOverallPath, minPath);
for (pii i : adjLists[centroid]) {
if (!vis[i.first]) {
decomp(i.first);
}
}
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n >> k;
for (int i = 0; i < n - 1; i++) {
int a, b, l; cin >> a >> b >> l;
adjLists[a].pb(pii(b, l));
adjLists[b].pb(pii(a, l));
}
treeDfs2(0, -1);
findAncestors();
calcSubtrees(0);
decomp(0);
cout << ((minOverallPath == 1e9) ? -1 : minOverallPath) << nl;
}