Problem E
Exchange Students
Determine the minimum number of exchanges needed to arrange the students in the photographerâ€™s preferred order, and find a suitable sequence of exchanges of this minimal length. The photographer only has time for at most $2\cdot 10^5$ exchanges. If more are needed, you only need to determine the first $2\cdot 10^5$ exchanges.
Input
The input consists of:

One line with an integer $n$ ($1\leq n \leq 3\cdot 10^5$), the number of students.

One line with $n$ integers $g_1, g_2, \ldots , g_ n$ ($1\leq g_ i\leq 10^9$), the heights of the students.

One line with $n$ integers $h_1, h_2, \ldots , h_ n$ ($1\leq h_ i\leq 10^9$), the order of heights the photographer prefers.
It is guaranteed that $(h_1, \ldots , h_ n)$ is a permutation of $(g_1, \ldots , g_ n)$.
Output
First output an integer $s$, the minimum number of exchanges needed. Then print $\min (s, 2\cdot 10^5)$ exchanges, each consisting of two integers $i$ and $j$, the onebased positions of the students that must be exchanged in this step.
If there are multiple valid solutions, you may print any one of them.
Sample Input 1  Sample Output 1 

3 2 1 3 3 1 2 
1 1 3 
Sample Input 2  Sample Output 2 

5 6 7 5 9 6 9 6 7 6 5 
4 3 4 4 5 1 2 1 3 