| # | Time | Username | Problem | Language | Result | Execution time | Memory |
|---|---|---|---|---|---|---|---|
| 1341128 | mehrzad | Triple Peaks (IOI25_triples) | C++20 | 0 ms | 0 KiB |
#include <bits/stdc++.h>
using namespace std;
long long count_triples(vector<int> H)
{
const int N = static_cast<int>(H.size());
long long cnt1 = 0, cnt2 = 0, cnt3 = 0, cnt4 = 0,
cnt5 = 0, cnt6 = 0, equal_cnt = 0;
/* ---------- assignment 1 ---------- */
for (int i = 0; i < N; ++i) {
int j = i + H[i];
if (j >= N) continue;
int b = H[j];
int k = j + b;
if (k >= N) continue;
if (H[k] == H[i] + b) ++cnt1;
}
/* ---------- assignment 2 ---------- */
for (int i = 0; i < N; ++i) {
int j = i + H[i];
if (j >= N) continue;
int b = H[j] - H[i];
if (b <= 0) continue;
int k = j + b;
if (k >= N) continue;
if (H[k] == b) ++cnt2;
}
/* ---------- assignment 3 ---------- */
for (int j = 0; j < N; ++j) {
int i = j - H[j];
if (i < 0) continue;
int b = H[i];
int k = j + b;
if (k >= N) continue;
if (H[k] == H[j] + b) ++cnt3;
}
/* ---------- assignment 5 ---------- */
for (int j = 0; j < N; ++j) {
int i = j - H[j];
if (i < 0) continue;
int b = H[i] - H[j];
if (b <= 0) continue;
int k = j + b;
if (k >= N) continue;
if (H[k] == b) ++cnt5;
}
/* ---------- assignment 6 ---------- */
for (int j = 0; j < N; ++j) {
int k = j + H[j];
if (k >= N) continue;
int a = H[k];
int i = j - a;
if (i < 0) continue;
if (H[i] == a + H[j]) ++cnt6;
}
/* ---------- assignment 4 (group i+H[i] = k-H[k]) ---------- */
// groups[T] = list of k such that k - H[k] == T (T = “key”)
unordered_map<int, vector<int>> groups;
groups.reserve(N * 2);
for (int k = 0; k < N; ++k) {
int T = k - H[k];
groups[T].push_back(k); // k grows, so each vector stays sorted
}
for (int i = 0; i < N; ++i) {
int T = i + H[i];
auto it = groups.find(T);
if (it == groups.end()) continue; // no k with the needed key
const vector<int>& ks = it->second;
// first k that is > i
auto posIter = upper_bound(ks.begin(), ks.end(), i);
int H_i = H[i];
for (auto kIt = posIter; kIt != ks.end(); ++kIt) {
int k = *kIt;
int j = k - H_i;
if (j >= N) break; // larger k → larger j, so we can stop
// i < j < k holds automatically for the chosen ks
if (H[j] == k - i) ++cnt4;
}
}
long long total = cnt1 + cnt2 + cnt3 + cnt4 + cnt5 + cnt6;
/* ---------- triples with equal distances (a = b) ----------
These triples were counted twice (once in the main total and
once in the equal‑distance special case), therefore we subtract
them once at the end. */
for (int i = 0; i < N; ++i) {
int a = H[i];
// case 1 : distance = a (i → j → k, with j = i+a, k = i+2a)
int j = i + a;
if (j < N) {
int k = i + 2 * a;
if (k < N) {
bool ok = (H[j] == a && H[k] == 2 * a) ||
(H[j] == 2 * a && H[k] == a);
if (ok) ++equal_cnt;
}
}
// case 2 : distance = 2a (i → j (a) → k (2a), but we treat a = H[i]/2)
if (a % 2 == 0) {
int a2 = a / 2;
if (a2 > 0) {
j = i + a2;
int k = i + a; // i + 2*a2 = i + a
if (j < N && k < N) {
if (H[j] == a2 && H[k] == a2) ++equal_cnt;
}
}
}
}
return total - equal_cnt;
}