CF27C.Unordered Subsequence

The sequence is called ordered if it is non-decreasing or non-increasing. For example, sequnces [3, 1, 1, 0] and [1, 2, 3, 100] are ordered, but the sequence [1, 3, 3, 1] is not. You are given a sequence of numbers. You are to find it's shortest subsequence which is not ordered.

A subsequence is a sequence that can be derived from the given sequence by deleting zero or more elements without changing the order of the remaining elements.

如果一个序列是非递减的或非递增的，则称该序列为有序的。例如，序列 [3, 1, 1, 0] 和 [1, 2, 3, 100] 是有序的，但序列 [1, 3, 3, 1] 不是有序的。你将得到一个数字序列，请找出其中最短的无序子序列。

子序列是指通过从原序列中删除零个或多个元素（不改变剩余元素的相对顺序）而得到的序列。

The first line of the input contains one integer n (1 ≤ n ≤ 105). The second line contains n space-separated integers — the given sequence. All numbers in this sequence do not exceed 106 by absolute value.

输入的第一行包含一个整数 $n$（$1 \leq n \leq 10^5$）。第二行包含 $n$ 个以空格分隔的整数——给定的序列。该序列中的所有数的绝对值均不超过 $10^6$。

If the given sequence does not contain any unordered subsequences, output 0. Otherwise, output the length k of the shortest such subsequence. Then output k integers from the range [1..n] — indexes of the elements of this subsequence. If there are several solutions, output any of them.

如果给定序列不包含任何无序子序列，则输出 0；否则，输出最短此类子序列的长度 $k$，然后输出 $k$ 个取值范围在 $[1..n]$ 内的整数——即该子序列中各元素的下标。若存在多个解，输出任意一个即可。