D题求hack数据

如题，自己测了半个小时了，通过率一直卡在96%，实在测不出来了。

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <vector>
#include <unordered_map>
#include <map>
#include <iomanip>
#include <queue>

using namespace std;

typedef long long LL;
typedef pair<int, int> PII;

int dx[4] = { -1, 1, 0, 0 };
int dy[4] = { 0, 0, -1, 1 };

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

    LL n, k;
    cin >> n >> k;
    vector<LL> a(n + 2);
    for (int i = 1; i <= n; ++i) cin >> a[i];
    
	// 假设最大能抽到x，有(0+1+2+...+x)<(k+x+1),化简得(k-2)*(k+1)<2*k
    // 不能相等
    LL l = 1, r = n - 1;
    while (l < r)
    {
        LL mid = (l + r + 1) / 2;
        if ((mid - 2) * (mid + 1) < 2 * k) l = mid;
        else r = mid - 1;
    }
    LL x = l + 1;

    vector<LL> preSum(n + 2);
    vector<LL> sufSum(n + 2);

    LL sum = 0;
    for (int i = 1; i <= n; ++i)
    {
        sum += a[i];
        preSum[i] = max(preSum[i - 1], sum);
    }
    sum = 0;
    for (int i = n; i >= 1; --i)
    {
        sum += a[i];
        sufSum[i] = max(sufSum[i + 1], sum);
    }

    LL ans = 0;
    for (int i = 0; i <= x; ++i)
    {
        ans = max(ans, preSum[i] + sufSum[n - x + 1 + i]);
    }
    cout << ans << '\n';
    return 0;
}

感觉代码还是比较简洁的