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문제

There are $N$ non-negative integers $a_1, a_2, \dots, a_N$ satisfying the following inequality $0 \le a_1 < a_2 < \cdots < a_N \le 10^{18}$. Jeehak wants to know the largest possible value of $a_{i+1} - a_i$ where $i$ ranges from $1$ to $N-1$. The input integers will not be given directly to Jeehak's program but will be accessible through a special funtion. See sections Implementation of your selected programming language for details.

Help Jeehak to implement a function to return the largest possible value of $a_{i+1} - a_i$ where $i$ ranges from $1$ to $N-1$.

구현

You need to implement one function findGap(T, N) that takes the following parameter and returns an integer of type long long:

  • T — the subtask number (1 or 2)
  • N — the number of given integers

Your function findGap can call function MinMax(s, t, &mn, &mx) where the first two parameters s and t are integers of type long long and the last two paramters &mn and &mx are pointers to integer variables of type long long, i.e., mn and mx are integer variables of type long long. When MinMax(s, t, &mn, &mx) returns, the variable mn will have the value of smallest $a_i$ larger than or equal to the value of s and the variable mx will have the value of largest $a_j$ smaller than or equal to the value of t. In case there are no input integers between s and t (inclusive), then both mn and mx will have the value -1. The value of s should be no larger than the value of t when MinMax is called. If this condition is not met, program will be terminated with a non-zero exit code.

In addition to the standard requirements (time and memory limits, no runtime errors, etc), your submission has to achieve the following in order to solve a testcase:

  • your function findGap must return the correct answer,
  • the cost $M$ associated with calls to function MinMax must not exceed the allowed limit.

예제

Consider the case where $N = 4$ and $a_1 = 2, a_2 = 3, a_3 = 6$, and $a_4 = 8$.

The answer, which is $3$, can be calculated and thus returned by findGap if the following calls to MinMax are made:

  • MinMax(1, 2, &mn, &mx) is called and mn and mx both have the value $2$.
  • MinMax(3, 7, &mn, &mx) is called and mn have the value $3$ and mx has the value $6$.
  • MinMax(8, 9, &mn, &mx) is called and mn and mx both have the value $8$.

제한

In allsubtasks the constraint $2 \le N \le 100\,000$ holds.

샘플 그레이더

The sample grader which can be downloaded from the scoring system will read data from standard input. The first line of input should contain two integers, subtask number $T$, and $N$. The next line should contain $N$ integers in ascending order. The sample grader will write to standard output the value returned by findGap in the first line and the value of $M$ appropriate for the subtask the input test case belongs to.

The following input describes the above example:

2 4
2 3 6 8

서브태스크 1 (30점)

Each call to MinMax will add $1$ to $M$. You will receive the fullscore for the subtask if $M \le \frac{N+1}{2}$ for all test cases.

서브태스크 2 (70점)

Let $k$ be the number of input integers larger than or equal to s and smaller than or equal to t in a call to MinMax. Each call to MinMax will add $k+1$ to $M$. The finalscore will be calculated by the following rule: Finalscore for the subtask is the minimum score you received among all test cases. For a test case, the score is 70 if $M \le 3N$ and the score is $\frac{60}{\sqrt{\frac{M}{N}+1}-1}$, otherwise.

첨부

제출할 수 있는 언어

C++17, C++14, C++20, C++14 (Clang), C++17 (Clang), C++20 (Clang)

채점 및 기타 정보

  • 예제는 채점하지 않는다.