# | Time | Username | Problem | Language | Result | Execution time | Memory |
---|---|---|---|---|---|---|---|
1251362 | tranvinhhuy2010 | Triple Peaks (IOI25_triples) | C++20 | 0 ms | 0 KiB |
//#include "triples.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int nmax = 2e5 + 5;
int n;
unordered_map <int, vector <int>> mk;
ll count_triples(vector <int> H) {
n = H.size();
ll cnt = 0;
for (int j=0; j<n; j++) {
// Hj = j - i
int i = j - H[j];
if (i>=0) {
int k1 = i + H[i], k2 = j + H[i];
if (k1<n && k1>j && H[k1]==k1-j) cnt++;
if (k2<n && k2>j && H[k2]==k2-i) cnt++;
}
// Hj = k - j
int k = j + H[j];
if (k<n) {
int i1 = j - H[k], i2 = k - H[k];
if (i1>=0 && i1<j && H[i1]==k-i1) cnt++;
if (i2>=0 && i2<j && H[i2]==j-i2) cnt++;
}
mk[j - H[j]].push_back(j);
}
for (int i=0; i<n; i++) {
int j = i + H[i];
if (j<n) {
int k = i + H[j];
if (k>j && H[k]==k-j) cnt++;
}
}
for (int i=0; i<n; i++) {
mk[i - H[i]].erase(remove(mk[i - H[i]].begin(), mk[i - H[i]].end(), i), mk[i - H[i]].end());
for (int k : mk[i + H[i]]) {
int j = i + H[k];
if (j<k && H[j]==k-i) cnt++;
}
}
return cnt;
}
vector<int> construct_range(int M, int K) {
return {1, 1, 1};
}
int main() {
cout << count_triples({4, 1, 4, 3, 2, 6, 1});
return 0;
}