Submission #1316684

#	Time	Username	Problem	Language	Result	Execution time	Memory
1316684		ezzzay	Triple Peaks (IOI25_triples)	C++17	35 / 100	2095 ms	37136 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;

    // pattern 1: j = i + H[i], k = j + H[j]
    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});
            }
        }
    }

    // pattern 2: j = i + H[i], k = i + H[j]
    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});
            }
        }
    }

    // pattern 3: k = i + H[i], j = k - H[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});
            }
        }
    }

    // pattern 4: k = i + H[i], j = i + H[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});
            }
        }
    }

    // pattern 5: i = j - H[j], k = j + H[i]
    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});
            }
        }
    }

    // pattern 6: k = j + H[j], i = k - H[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});
            }
        }
    }

    // --- Missing symmetric case: j = i + H[k], k = i + H[j]
    // That is equivalent to j + H[j] == k + H[k]. Group indices by s = idx + H[idx]
    // and iterate pairs within each group to find (j,k) with same s.
    // (This recovers triples like (1,3,4) in the sample.)
    vector<vector<int>> groups(2 * n + 5);
    for (int idx = 0; idx < n; ++idx) {
        int s = idx + h[idx];
        groups[s].pb(idx);
    }
    for (const auto &vec : groups) {
        int L = vec.size();
        for (int a = 0; a < L; ++a) {
            int j = vec[a];
            for (int b = a + 1; b < L; ++b) {
                int k = vec[b];
                int i = k - h[j]; // from k = i + H[j] -> i = k - H[j]
                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});
                }
            }
        }
    }

    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:138:1: warning: no return statement in function returning non-void [-Wreturn-type]
  138 | }
      | ^

• Subtask 0: 0 / 0
• Subtask 1: 8 / 8
• Subtask 2: 6 / 6
• Subtask 3: 10 / 10
• Subtask 4: 11 / 11
• Subtask 5: 0 / 16
• Subtask 6: 0 / 19
• Subtask 7: 0 / 5
• Subtask 8: 0 / 5
• Subtask 9: 0 / 5
• Subtask 10: 0 / 5
• Subtask 11: 0 / 5
• Subtask 12: 0 / 5