66 lines
1.5 KiB
Markdown
66 lines
1.5 KiB
Markdown
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# B. Black Cells
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[Codeforces](https://codeforces.com/contest/2026/problem/B)
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You are given a strip divided into cells, numbered from left to right from 0 to 1018. Initially, all cells are white.
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You can perform the following operation: choose two white cells `i` and `j`,
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such that `i` ≠ `j` and |`i` − `j`| ≤ `k`, and paint them black.
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A list `a` is given. All cells from this list must be painted black.
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Additionally, at most one cell that is not in this list can also be painted black.
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Your task is to determine the minimum value of `k` for which this is possible.
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## Input
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The first line contains a single integer `t` (1 ≤ `t` ≤ 500) — the number of test cases.
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The first line of each test case contains a single integer `n` (1 ≤ `n` ≤ 2000).
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The second line contains `n` integers `a1`, `a2`, ... , `an` (0 < `ai`< 1018; `ai` < `ai` + 1).
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Additional constraint on the input: the sum of `n` across all test cases does not exceed 2000.
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## Output
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For each test case, print a single integer — the minimum value of `k`
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for which it is possible to paint all the given cells black.
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## Example
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Input
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```
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4
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2
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1 2
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1
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7
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3
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2 4 9
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5
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1 5 8 10 13
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```
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Output
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```
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1
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1
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2
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3
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```
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## Note
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In the first example, with `k` = 1 , it is possible to paint the cells (1, 2).
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In the second example, with `k` = 1, it is possible to paint the cells (7, 8).
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In the third example, with `k` = 2, it is possible to paint the cells (2, 4) and (8, 9).
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In the fourth example, with `k` = 3, it is possible to paint the cells (0, 1), (5, 8) and (10, 13).
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