P10854 [MX-X2-T3] "Cfz Round 4" Ninelie

Original problem link: 。 ---  Along the one-sided endless echoing melody, it flows through the streets before my eyes, together with a love that has come to an end, fading farther and farther away. That ideal blueprint that cannot be conveyed grows more and more twisted; the silent resistance awakens at this very moment, and the impulse also arrives late at this very moment. Broken cries and beautiful dreams; the ideal is left with only a decorative facade. Even if the city is willing to be drowned in noise and clamor, I will keep singing loudly and give up everything that controls me. So I only wish that silence can echo once again. > No need to fear; dawn has already arrived.

Given a $01$ sequence $a_1, \ldots, a_n$ of length $n$ and a positive integer $r$. You can perform operations on the sequence $a$. In each operation, you need to choose an index $p$ such that $p$ is $1$ or $n$ or $a_{p-1}\neq a_{p+1}$, and then flip $a_p$ (that is, change $0$ to $1$, and change $1$ to $0$). Please make the sequence $a$ become all $0$'s or all $1$'s within $r$ operations. **You do not need to minimize the number of operations**. If it cannot be done, you need to report that there is no solution. **The testdata guarantees that $\bm{r = 2 \times 10^6}$ or $\bm{10^6}$. For details, please see the Constraints section.**

The first line contains two positive integers $n, r$. The second line contains $n$ integers $a_1, \ldots, a_n$.

If it is impossible to make the sequence $a$ become all $0$'s or all $1$'s within $r$ operations, output one line with one integer $-1$. If there exists a constructive solution, output two lines: - The first line contains a non-negative integer $m$, meaning the number of operations; you need to ensure $m\le r$, **and you do not need to minimize $\bm m$**. - The second line contains $m$ positive integers, representing the index $p$ chosen in each operation in order.

**[Sample Explanation #1]** The sequence $a$ after each operation is, respectively: - $[0,1,1,0]$； - $[0,1,1,1]$； - $[1,1,1,1]$。 At this time, all elements in the sequence $a$ are the same. **[Constraints]** For all testdata, $2\le n\le 2\times 10^3$, $a_i\in\{0,1\}$, and $r = 2 \times 10^6$ or $10^6$. **This problem uses bundled tests.** - Subtask 1 (20 points): $n\le 10$, $r=2\times 10^6$. - Subtask 2 (30 points): $r=2\times 10^6$. - Subtask 3 (50 points): $r=10^6$. Translated by ChatGPT 5