How do you think what's the input-data in test-2? I did tested my program around 10 times :) but i didn't find mistake((

UPD: N = 1 )))
you mustn't test borders-cases in input data. You must check your algorithm.
In this case i have "out of range" (because v_arr has length = 0, but in this program i don't check it and i address to zero index).
If check border-case this algorithm is working

My program:
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#include <iostream>
#include <cmath>

struct Point {
    int64_t x;
    int64_t y;
};

struct Vector {
    double r;
    double angle;
};

int cmp(const void *a, const void *b){
    Vector* v1 = (Vector*)a;
    Vector* v2 = (Vector*)b;
    double ans1 = ((v1->angle) - (v2->angle));
    if (ans1 < 0){
        return -1;
    } else if (ans1 > 0){
        return 1;
    }
    double ans2 = ((v1->r) - (v2->r));
    if (ans2 < 0){
        return -1;
    } else if (ans2 > 0){
        return 1;
    }
    return 0;
}

int main()
{
    int N;
    std::cin >> N;
    Point p_arr[N];
    Vector v_arr[N-1];
    double dist = 0;
    int64_t dx, dy;
    for (int i = 0; i < N; ++i){
        std::cin >> p_arr[i].x >> p_arr[i].y;
    }
    for (int i = 0; i < N; ++i){
        for (int j = 0; j < i; ++j){
            dx = p_arr[j].x - p_arr[i].x;
            dy = p_arr[j].y - p_arr[i].y;
            v_arr[j].r = sqrt(dx*dx + dy*dy);
            v_arr[j].angle = atan2(dy, dx);
        }
        for (int j = i+1; j < N; ++j){
            dx = p_arr[j].x - p_arr[i].x;
            dy = p_arr[j].y - p_arr[i].y;
            v_arr[j-1].r = sqrt(dx*dx + dy*dy);
            v_arr[j-1].angle = atan2(dy, dx);
        }
        qsort(v_arr, N-1, sizeof(Vector), cmp);
        for (int j = N-2; j > 0; --j){
            v_arr[j].angle -= v_arr[j-1].angle;
        }
        dist += v_arr[0].r;
        for (int j = 1; j < N-1; ++j){
            if (v_arr[j].angle != 0){
                dist += v_arr[j].r;
            }
        }
    }
    printf("%.0f", (dist / 2));
}
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Edited by author 20.08.2020 00:55