等差子序列 - 题目

#469. 等差子序列

统计

给出一个长度为 $N$ 的正整数序列，问是否存在一个长度不小于三的等差子序列。

输入格式

第一行一个正整数 $T$，表示数据组数。

接下来 $T$ 组数据，每组数据第一行一个正整数 $N$，表示序列长度，接下来第二行有 $N$ 个正整数，依次表示序列中的数。

输出格式

对于每组数据，输出单独的一行 YES 或 NO。

样例数据

样例 1 输入

3
4
4 3 2 1
2
1 100
5
1 17 9 18 17

样例 1 输出

YES
NO
YES

子任务

对于 $20\%$的数据：$N\le 100$。

对于 $40\%$的数据：$N\le 10^3$。

对于 $100\%$的数据：$1\le T \le 10$，$1\le N\le 2\times 10^4$，序列中的数 $\le 2\times 10^4$。

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