H. Set Merging
time limit per test
4 seconds
memory limit per test
256 megabytes
standard input
standard output

You are given a permutation $$$a_1, a_2, \dots, a_n$$$ of numbers from $$$1$$$ to $$$n$$$. Also, you have $$$n$$$ sets $$$S_1,S_2,\dots, S_n$$$, where $$$S_i=\{a_i\}$$$. Lastly, you have a variable $$$cnt$$$, representing the current number of sets. Initially, $$$cnt = n$$$.

We define two kinds of functions on sets:

$$$f(S)=\min\limits_{u\in S} u$$$;

$$$g(S)=\max\limits_{u\in S} u$$$.

You can obtain a new set by merging two sets $$$A$$$ and $$$B$$$, if they satisfy $$$g(A)<f(B)$$$ (Notice that the old sets do not disappear).

Formally, you can perform the following sequence of operations:

  • $$$cnt\gets cnt+1$$$;

  • $$$S_{cnt}=S_u\cup S_v$$$, you are free to choose $$$u$$$ and $$$v$$$ for which $$$1\le u, v < cnt$$$ and which satisfy $$$g(S_u)<f(S_v)$$$.

You are required to obtain some specific sets.

There are $$$q$$$ requirements, each of which contains two integers $$$l_i$$$,$$$r_i$$$, which means that there must exist a set $$$S_{k_i}$$$ ($$$k_i$$$ is the ID of the set, you should determine it) which equals $$$\{a_u\mid l_i\leq u\leq r_i\}$$$, which is, the set consisting of all $$$a_i$$$ with indices between $$$l_i$$$ and $$$r_i$$$.

In the end you must ensure that $$$cnt\leq 2.2\times 10^6$$$. Note that you don't have to minimize $$$cnt$$$. It is guaranteed that a solution under given constraints exists.


The first line contains two integers $$$n,q$$$ $$$(1\leq n \leq 2^{12},1 \leq q \leq 2^{16})$$$  — the length of the permutation and the number of needed sets correspondently.

The next line consists of $$$n$$$ integers $$$a_1,a_2,\cdots, a_n$$$ ($$$1\leq a_i\leq n$$$, $$$a_i$$$ are pairwise distinct)  — given permutation.

$$$i$$$-th of the next $$$q$$$ lines contains two integers $$$l_i,r_i$$$ $$$(1\leq l_i\leq r_i\leq n)$$$, describing a requirement of the $$$i$$$-th set.


It is guaranteed that a solution under given constraints exists.

The first line should contain one integer $$$cnt_E$$$ $$$(n\leq cnt_E\leq 2.2\times 10^6)$$$, representing the number of sets after all operations.

$$$cnt_E-n$$$ lines must follow, each line should contain two integers $$$u$$$, $$$v$$$ ($$$1\leq u, v\leq cnt'$$$, where $$$cnt'$$$ is the value of $$$cnt$$$ before this operation), meaning that you choose $$$S_u$$$, $$$S_v$$$ and perform a merging operation. In an operation, $$$g(S_u)<f(S_v)$$$ must be satisfied.

The last line should contain $$$q$$$ integers $$$k_1,k_2,\cdots,k_q$$$ $$$(1\leq k_i\leq cnt_E)$$$, representing that set $$$S_{k_i}$$$ is the $$$i$$$th required set.

Please notice the large amount of output.

3 2
1 3 2
2 3
1 3
3 2
1 3
5 2
4 6 
2 4
2 1
1 2
1 2
1 2
1 1
2 1
2 1
2 1
5 3 3 1

In the first sample:

We have $$$S_1=\{1\},S_2=\{3\},S_3=\{2\}$$$ initially.

In the first operation, because $$$g(S_3)=2<f(S_2)=3$$$, we can merge $$$S_3,S_2$$$ into $$$S_4=\{2,3\}$$$.

In the second operation, because $$$g(S_1)=1<f(S_3)=2$$$, we can merge $$$S_1,S_3$$$ into $$$S_5=\{1,2\}$$$.

In the third operation, because $$$g(S_5)=2<f(S_2)=3$$$, we can merge $$$S_5,S_2$$$ into $$$S_6=\{1,2,3\}$$$.

For the first requirement, $$$S_4=\{2,3\}=\{a_2,a_3\}$$$, satisfies it, thus $$$k_1=4$$$.

For the second requirement, $$$S_6=\{1,2,3\}=\{a_1,a_2,a_3\}$$$, satisfies it, thus $$$k_2=6$$$

Notice that unused sets, identical sets, outputting the same set multiple times, and using sets that are present initially are all allowed.