Submission #1250182

#	Time	Username	Problem	Language	Result	Execution time	Memory
1250182		s4dz	Triple Peaks (IOI25_triples)	C++20	0 / 100	27 ms	15684 KiB

triples

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
//sub4:
std::vector<int> construct_range(int M, int K)
{
    return{};
}
/*long long count_triples(vector<int> H)
{
    int n = H.size();
    ll ans = 0;
    for (int k = 0; k < n; k++)
    {
        int c = H[k];
        int i = k - c;
        if (i < 0 || i >= n) continue;

        int a = H[i];
        if (a > c - a) continue;

        int need = c - a;
        int j1   = i + a;
        int j2   = k - a;
        if (i < j1 && j1 < k && H[j1] == need) ans++;
        if (j2 != j1 && i < j2 && j2 < k && H[j2] == need) ans++;
    }
    return ans;
}*/
ll count_triples(vector<int> H)
{
    int N = H.size();
    ll ans = 0;
    for (int i = 0; i < N; i++)
    {
        int k = i + H[i];
        if (k >= N) continue;
        // if H[k] == j - i  → j = i + H[k]
        {
            int j = i + H[k];
            if (j > i && j < k && H[j] == k - j)
                ans++;
        }
        // if H[k] == k - j  → j = k - H[k]
        {
            int j = k - H[k];
            if (j > i && j < k && H[j] == j - i)
                ans++;
        }
    }
    for (int k = 0; k < N; k++)
    {
        int i = k - H[k];
        if (i < 0) continue;
        {
            int j = i + H[i];
            if (j > i && j < k && H[j] == k - j)
                ans++;
        }
        {
            int j = k - H[i];
            if (j > i && j < k && H[j] == j - i)
                ans++;
        }
    }
    for (int i = 0; i < N; i++)
    {
        int j = i + H[i];
        if (j >= N) continue;
        int k = i + H[j];
        if (k < N && H[k] == k - j)
            ans++;
    }
    int T = int(sqrt(N));
    vector<vector<int>> groups(2*N+1);
    for (int i = 0; i < N; i++)
    {
        int x = H[i] - i + N;
        groups[x].push_back(i);
    }

    for (int gx = 0; gx <= 2*N; gx++)
    {
        auto &vec = groups[gx];
        if (vec.empty()) continue;
        int C = gx - N;

        if ((int)vec.size() <= T)
        {
            for (int a = 0; a < (int)vec.size(); a++)
            {
                for (int b = a+1; b < (int)vec.size(); b++)
                {
                    int i = vec[a], j = vec[b];
                    int k = i + j + C;
                    if (k < N && j < k && H[k] == j - i)
                        ans++;
                }
            }
        }
        else
        {
            for (int k = 0; k < N; k++)
            {
                int sum = k - C;
                int diff = H[k];
                if (((sum + diff) & 1) != 0) continue;
                int j = (sum + diff) >> 1;
                int i = j - diff;
                if (0 <= i && i < j && j < k)
                {
                    if (H[i] - i == C && H[j] - j == C) ans++;
                }
            }
        }
    }

    return ans;
}

• Subtask 0: 0 / 0
• Subtask 1: 0 / 8
• Subtask 2: 0 / 6
• Subtask 3: 0 / 10
• Subtask 4: 0 / 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