Submission #1250056

#	Time	Username	Problem	Language	Result	Execution time	Memory
1250056		testacc11	Triple Peaks (IOI25_triples)	C++20	Compilation error	0 ms	0 KiB

triples

// triples.cpp
#include <vector>
using namespace std;
using ll = long long;

// Part I: count all mythical triples in O(N) time and O(N) memory.
ll count_triples(const vector<int>& H) {
    int N = H.size();
    // L1[j] = all i<j such that H[i] = j-i
    vector<vector<int>> L1(N);
    // S[T] = all k such that k+H[k] = T
    vector<vector<int>> S(2 * N);
    for (int i = 0; i < N; i++) {
        int t = i + H[i];
        if (t < N) L1[t].push_back(i);
        S[t].push_back(i);
    }

    ll ans = 0;
    for (int j = 0; j < N; j++) {
        int hj = H[j];

        // Case A: H[j] = d1 = j - i
        {
            int i = j - hj;
            if (i >= 0) {
                int hi = H[i];
                int k = j + hi;
                if (k < N && hi + hj == H[k])
                    ans++;
            }
        }

        // Case B: H[j] = d2 = k - j
        {
            int k = j + hj;
            if (k < N) {
                int hk = H[k];
                int i = k - hk;
                if (i >= 0 && i < j && hk - hj == H[i])
                    ans++;
            }
        }

        // Case C1: H[j] = d3, with H[i]=d1 and H[k]=d2
        for (int i : L1[j]) {
            int hi = H[i];
            int k  = i + hj;
            if (k > j && k < N && H[k] == hj - hi)
                ans++;
        }

        // Case C2: H[j] = d3, with H[k]=d1 and H[i]=d2
        int Tj = j + hj;
        if (Tj < (int)S.size()) {
            for (int k : S[Tj]) {
                if (k <= j) continue;
                int i = k - hj;
                if (i >= 0 && i < j && H[i] == k - j)
                    ans++;
            }
        }
    }
    return ans;
}

// Part II stub (if needed by grader)
vector<int> construct_range(int M, int K) {
    return vector<int>();  // not used for Part I
}

Compilation message (stderr)

/usr/bin/ld: /tmp/cctUKkWu.o: in function `main':
grader.cpp:(.text.startup+0x37b): undefined reference to `count_triples(std::vector<int, std::allocator<int> >)'
collect2: error: ld returned 1 exit status