Submission #1250048

#	Time	Username	Problem	Language	Result	Execution time	Memory
1250048		testacc11	Triple Peaks (IOI25_triples)	C++20	Compilation error	0 ms	0 KiB

triples

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int part;
    if(!(cin >> part)) return 0;
    if(part != 1){
        // This is Part I only.
        return 0;
    }

    int N;
    cin >> N;
    vector<int> H(N);
    for(int i = 0; i < N; i++){
        cin >> H[i];
    }

    // Precompute:
    //  L1[j] = all i < j with i + H[i] == j  (so H[i] = j - i)
    //  S[T]  = all k with k + H[k] == T
    vector<vector<int>> L1(N);
    vector<vector<int>> S(N + N);  // k+H[k] in [0..2N-2]
    for(int i = 0; i < N; i++){
        int j1 = i + H[i];
        if(j1 < N) L1[j1].push_back(i);
        int T = i + H[i];
        S[T].push_back(i);
    }

    ll ans = 0;
    // Main loop over the “middle” peak j
    for(int j = 0; j < N; j++){
        int hj = H[j];

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

        // Case C1: H[j] = d3 = (k - i), with H[i] = d1 = j - i
        //   ⇒ i in L1[j], then k = i + H[j], and check H[k] = d2 = H[j] - H[i].
        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 = (k - i), with H[k] = d1 = j - i
        //   ⇒ all k with k + H[k] = j + H[j]  (so H[k] = (j+H[j]) - k = j - (k-j) = d1),
        //      then set i = k - H[j] and check H[i] = d2 = k - j.
        int Tj = j + hj;
        if(Tj < (int)S.size()){
            for(int k : S[Tj]) {
                if(k <= j) continue;
                int i = k - hj;
                if(i < j && i >= 0 && H[i] == k - j) {
                    ans++;
                }
            }
        }
    }

    cout << ans << "\n";
    return 0;
}

Compilation message (stderr)

/usr/bin/ld: /tmp/ccLErIX1.o: in function `main':
grader.cpp:(.text.startup+0x0): multiple definition of `main'; /tmp/cc3a8lN0.o:triples.cpp:(.text.startup+0x0): first defined here
/usr/bin/ld: /tmp/ccLErIX1.o: in function `main':
grader.cpp:(.text.startup+0x18a): undefined reference to `construct_range(int, int)'
/usr/bin/ld: grader.cpp:(.text.startup+0x37b): undefined reference to `count_triples(std::vector<int, std::allocator<int> >)'
collect2: error: ld returned 1 exit status