Submission #1316688

#	Time	Username	Problem	Language	Result	Execution time	Memory
1316688		ezzzay	Triple Peaks (IOI25_triples)	C++17	11 / 100	152 ms	68348 KiB

triples

//#include "triples.h"
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
long long count_triples(vector<int> H) {
    vector<int> h;
    for (auto a : H) h.pb(a);
    set<vector<int>> ST;
    int n = H.size();
    long long cnt = 0;

    // --- six direct patterns (safe bounds + explicit i<j<k checks) ---
    for (int i = 0; i < n; ++i) {
        int j = i + h[i];
        if (j < n) {
            int k = j + h[j];
            if (k < n && i < j && j < k) {
                multiset<int> st = {H[i], H[j], H[k]};
                if (st.find(j - i) != st.end()) st.erase(st.find(j - i));
                if (st.find(k - i) != st.end()) st.erase(st.find(k - i));
                if (st.find(k - j) != st.end()) st.erase(st.find(k - j));
                if (st.empty()) ST.insert({i, j, k});
            }
        }
    }

    for (int i = 0; i < n; ++i) {
        int j = i + h[i];
        if (j < n) {
            int k = i + h[j];
            if (k < n && i < j && j < k) {
                multiset<int> st = {H[i], H[j], H[k]};
                if (st.find(j - i) != st.end()) st.erase(st.find(j - i));
                if (st.find(k - i) != st.end()) st.erase(st.find(k - i));
                if (st.find(k - j) != st.end()) st.erase(st.find(k - j));
                if (st.empty()) ST.insert({i, j, k});
            }
        }
    }

    for (int i = 0; i < n; ++i) {
        int k = i + h[i];
        if (k < n) {
            int j = k - h[k];
            if (j >= 0 && i < j && j < k) {
                multiset<int> st = {H[i], H[j], H[k]};
                if (st.find(j - i) != st.end()) st.erase(st.find(j - i));
                if (st.find(k - i) != st.end()) st.erase(st.find(k - i));
                if (st.find(k - j) != st.end()) st.erase(st.find(k - j));
                if (st.empty()) ST.insert({i, j, k});
            }
        }
    }

    for (int i = 0; i < n; ++i) {
        int k = i + h[i];
        if (k < n) {
            int j = i + h[k];
            if (j < n && i < j && j < k) {
                multiset<int> st = {H[i], H[j], H[k]};
                if (st.find(j - i) != st.end()) st.erase(st.find(j - i));
                if (st.find(k - i) != st.end()) st.erase(st.find(k - i));
                if (st.find(k - j) != st.end()) st.erase(st.find(k - j));
                if (st.empty()) ST.insert({i, j, k});
            }
        }
    }

    for (int j = 0; j < n; ++j) {
        int i = j - h[j];
        if (i >= 0) {
            int k = j + h[i];
            if (k < n && i < j && j < k) {
                multiset<int> st = {H[i], H[j], H[k]};
                if (st.find(j - i) != st.end()) st.erase(st.find(j - i));
                if (st.find(k - i) != st.end()) st.erase(st.find(k - i));
                if (st.find(k - j) != st.end()) st.erase(st.find(k - j));
                if (st.empty()) ST.insert({i, j, k});
            }
        }
    }

    for (int j = 0; j < n; ++j) {
        int k = j + h[j];
        if (k < n) {
            int i = k - h[k];
            if (i >= 0 && i < j && j < k) {
                multiset<int> st = {H[i], H[j], H[k]};
                if (st.find(j - i) != st.end()) st.erase(st.find(j - i));
                if (st.find(k - i) != st.end()) st.erase(st.find(k - i));
                if (st.find(k - j) != st.end()) st.erase(st.find(k - j));
                if (st.empty()) ST.insert({i, j, k});
            }
        }
    }

    // --- Optimized handling of the symmetric case (no O(g^2) pairs) ---
    // Build groups by s = idx + H[idx] and membership hash-sets.
    int Smax = 2 * n + 5;
    vector<vector<int>> groups(Smax);
    unordered_map<int, unordered_set<int>> groups_set; groups_set.reserve(n * 2);
    for (int idx = 0; idx < n; ++idx) {
        int s = idx + h[idx];
        groups[s].pb(idx);
    }
    for (int s = 0; s < Smax; ++s) {
        if (!groups[s].empty()) {
            unordered_set<int> st; st.reserve(groups[s].size() * 2 + 1);
            for (int x : groups[s]) st.insert(x);
            groups_set[s] = std::move(st);
        }
    }

    // For each j, iterate i in groups[j] (i + H[i] == j).
    // For each such i compute k = i + H[j] and check if k in groups[s_j], then validate triple.
    for (int j = 0; j < n; ++j) {
        int s_j = j + h[j];
        if (s_j < 0 || s_j >= Smax) continue;
        if (groups[j].empty()) continue;            // no i such that i + H[i] == j
        if (groups_set.find(s_j) == groups_set.end()) continue; // no k with s = s_j
        auto &target_set = groups_set[s_j];
        for (int i : groups[j]) {
            int k = i + h[j];
            if (k <= j || k >= n) continue; // need i < j < k
            if (target_set.find(k) == target_set.end()) continue;
            // final verification (multiset check) to be safe
            multiset<int> st = {H[i], H[j], H[k]};
            if (st.find(j - i) != st.end()) st.erase(st.find(j - i));
            if (st.find(k - i) != st.end()) st.erase(st.find(k - i));
            if (st.find(k - j) != st.end()) st.erase(st.find(k - j));
            if (st.empty()) ST.insert({i, j, k});
        }
    }

    cnt = (long long)ST.size();
    return cnt;
}




vector<int> construct_range(int M, int K) {
    
}

Compilation message (stderr)

triples.cpp: In function 'std::vector<int> construct_range(int, int)':
triples.cpp:145:1: warning: no return statement in function returning non-void [-Wreturn-type]
  145 | }
      | ^

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