C - The Kth Time Query

Score : $300$ points

Problem Statement

We have a sequence of $N$ numbers: $A = (a_1, a_2, \dots, a_N)$.
Process the $Q$ queries explained below.

• Query $i$: You are given a pair of integers $(x_i, k_i)$. Let us look at the elements of $A$ one by one from the beginning: $a_1, a_2, \dots$ Which element will be the $k_i$-th occurrence of the number $x_i$?
  Print the index of that element, or $-1$ if there is no such element.

Constraints

• $1 \leq N \leq 2 \times 10^5$
• $1 \leq Q \leq 2 \times 10^5$
• $0 \leq a_i \leq 10^9$ $(1 \leq i \leq N)$
• $0 \leq x_i \leq 10^9$ $(1 \leq i \leq Q)$
• $1 \leq k_i \leq N$ $(1 \leq i \leq Q)$
• All values in input are integers.

Input

Input is given from Standard Input in the following format:

$N$ $Q$

$a_1$ $a_2$ $\dots$ $a_N$

$x_1$ $k_1$

$x_2$ $k_2$

$\vdots$

$x_Q$ $k_Q$

Output

Print $Q$ lines. The $i$-th line should contain the answer to Query $i$.

6 8
1 1 2 3 1 2
1 1
1 2
1 3
1 4
2 1
2 2
2 3
4 1

1
2
5
-1
3
6
-1
-1

$1$ occurs in $A$ at $a_1, a_2, a_5$. Thus, the answers to Query $1$ through $4$ are $1, 2, 5, -1$ in this order.

3 2
0 1000000000 999999999
1000000000 1
123456789 1

2
-1