| # | Time | Username | Problem | Language | Result | Execution time | Memory |
|---|---|---|---|---|---|---|---|
| 1276504 | mehrzad | Obstacles for a Llama (IOI25_obstacles) | C++17 | 0 ms | 0 KiB |
include <bits/stdc++.h>
using namespace std;
/*** segment tree for range maximum ***/
struct SegTree {
int n;
vector<int> seg;
SegTree() {}
SegTree(const vector<int> &a) { build(a); }
void build(const vector<int> &a) {
int sz = (int)a.size();
n = 1;
while (n < sz) n <<= 1;
seg.assign(2 * n, INT_MIN);
for (int i = 0; i < sz; ++i) seg[n + i] = a[i];
for (int i = n - 1; i > 0; --i) seg[i] = max(seg[i << 1], seg[i << 1 | 1]);
}
// inclusive query [l, r]
int query(int l, int r) const {
l += n; r += n;
int res = INT_MIN;
while (l <= r) {
if (l & 1) res = max(res, seg[l++]);
if (!(r & 1)) res = max(res, seg[r--]);
l >>= 1; r >>= 1;
}
return res;
}
};
/*** DSU ***/
struct DSU {
vector<int> p, r;
DSU() {}
DSU(int n) { init(n); }
void init(int n) {
p.resize(n);
r.assign(n, 0);
iota(p.begin(), p.end(), 0);
}
int find(int x) {
if (p[x] == x) return x;
return p[x] = find(p[x]);
}
void unite(int a, int b) {
a = find(a); b = find(b);
if (a == b) return;
if (r[a] < r[b]) swap(a, b);
p[b] = a;
if (r[a] == r[b]) ++r[a];
}
};
/*** global data for the queries ***/
static vector<int> colToSeed; // -1 for non‑seed, otherwise seed index
static DSU dsu;
static vector<int> seedPos; // column index of each seed (ordered by column)
static vector<int> maxDepthSeed; // maxDepth for each seed (by seed index)
/*** helpers ***/
static vector<int> prefMin; // size N
static vector<int> prefMax; // size N
static SegTree segH; // range maximum over H
/* binary search: largest i with prefMin[i] > h (seed guarantees existence) */
static int computeMaxDepth(int h) {
int lo = 0, hi = (int)prefMin.size(); // hi == N means not found
while (lo < hi) {
int mid = lo + (hi - lo) / 2;
if (prefMin[mid] > h) lo = mid + 1;
else hi = mid;
}
// first index where prefMin <= h is 'lo'
return lo - 1; // may become N-1 if never <= h
}
/*** required functions ***/
void initialize(vector<int> T, vector<int> H) {
int N = (int)T.size();
int M = (int)H.size();
/* prefix minima and maxima of temperatures */
prefMin.resize(N);
prefMax.resize(N);
prefMin[0] = T[0];
prefMax[0] = T[0];
for (int i = 1; i < N; ++i) {
prefMin[i] = min(prefMin[i - 1], T[i]);
prefMax[i] = max(prefMax[i - 1], T[i]);
}
/* segment tree on H for interval maximum queries */
segH.build(H);
/* seeds */
seedPos.clear();
colToSeed.assign(M, -1);
for (int j = 0; j < M; ++j) {
if (H[j] < T[0]) {
colToSeed[j] = (int)seedPos.size();
seedPos.push_back(j);
}
}
int K = (int)seedPos.size();
dsu.init(K);
maxDepthSeed.assign(K, -1);
/* maxDepth for each seed */
for (int idx = 0; idx < K; ++idx) {
int col = seedPos[idx];
int h = H[col];
maxDepthSeed[idx] = computeMaxDepth(h);
}
/* order seeds by decreasing maxDepth */
vector<int> order(K);
iota(order.begin(), order.end(), 0);
sort(order.begin(), order.end(),
[&](int a, int b) {
return maxDepthSeed[a] > maxDepthSeed[b];
});
/* active set of seed columns (ordered by column) */
set<int> active; // stores column numbers of already inserted seeds
for (int idx : order) {
int col = seedPos[idx];
int d = maxDepthSeed[idx]; // depth up to which this seed works
auto it = active.insert(col).first;
// left neighbour
if (it != active.begin()) {
auto itL = prev(it);
int colL = *itL;
int idxL = colToSeed[colL];
int intervalMax = segH.query(min(colL, col), max(colL, col));
if (prefMax[d] > intervalMax) dsu.unite(idx, idxL);
}
// right neighbour
auto itR = next(it);
if (itR != active.end()) {
int colR = *itR;
int idxR = colToSeed[colR];
int intervalMax = segH.query(min(col, colR), max(col, colR));
if (prefMax[d] > intervalMax) dsu.unite(idx, idxR);
}
}
}
/* L and R are always 0 and M-1, they are ignored */
bool can_reach(int L, int R, int S, int D) {
if (S == D) return true;
int idS = colToSeed[S];
int idD = colToSeed[D];
if (idS == -1 || idD == -1) return false; // should not happen
return dsu.find(idS) == dsu.find(idD);
}