A12700 | Candies!

Consider a sequence of digits of length $2^k$ $[a_1, a_2, \ldots, a_{2^k}]$ . We perform the following operation with it: replace pairs $(a_{2i+1}, a_{2i+2})$ with $(a_{2i+1} + a_{2i+2})\bmod 10$ for $0\le i<2^{k-1}$ . For every $i$ where $a_{2i+1} + a_{2i+2}\ge 10$ we get a candy! As a result, we will get a sequence of length $2^{k-1}$ .

Less formally, we partition sequence of length $2^k$ into $2^{k-1}$ pairs, each consisting of 2 numbers: the first pair consists of the first and second numbers, the second of the third and fourth $\ldots$ , the last pair consists of the ( $2^k-1$ )-th and ( $2^k$ )-th numbers. For every pair such that sum of numbers in it is at least $10$ , we get a candy. After that, we replace every pair of numbers with a remainder of the division of their sum by $10$ (and don't change the order of the numbers).

Perform this operation with a resulting array until it becomes of length $1$ . Let $f([a_1, a_2, \ldots, a_{2^k}])$ denote the number of candies we get in this process.

For example: if the starting sequence is $[8, 7, 3, 1, 7, 0, 9, 4]$ then:

After the first operation the sequence becomes $[(8 + 7)\bmod 10, (3 + 1)\bmod 10, (7 + 0)\bmod 10, (9 + 4)\bmod 10]$ $=$ $[5, 4, 7, 3]$ , and we get $2$ candies as $8 + 7 \ge 10$ and $9 + 4 \ge 10$ .

After the second operation the sequence becomes $[(5 + 4)\bmod 10, (7 + 3)\bmod 10]$ $=$ $[9, 0]$ , and we get one more candy as $7 + 3 \ge 10$ .

After the final operation sequence becomes $[(9 + 0) \bmod 10]$ $=$ $[9]$ .

Therefore, $f([8, 7, 3, 1, 7, 0, 9, 4]) = 3$ as we got $3$ candies in total.

You are given a sequence of digits of length $n$ $s_1, s_2, \ldots s_n$ . You have to answer $q$ queries of the form $(l_i, r_i)$ , where for $i$ -th query you have to output $f([s_{l_i}, s_{l_i+1}, \ldots, s_{r_i}])$ . It is guaranteed that $r_i-l_i+1$ is of form $2^k$ for some nonnegative integer $k$ .

The first line contains a single integer $n$ ( $1 \le n \le 10^5$ ) — the length of the sequence.

The second line contains $n$ digits $s_1, s_2, \ldots, s_n$ ( $0 \le s_i \le 9$ ).

The third line contains a single integer $q$ ( $1 \le q \le 10^5$ ) — the number of queries.

Each of the next $q$ lines contains two integers $l_i$ , $r_i$ ( $1 \le l_i \le r_i \le n$ ) — $i$ -th query. It is guaranteed that $r_i-l_i+1$ is a nonnegative integer power of $2$ .

Output $q$ lines, in $i$ -th line output single integer — $f([s_{l_i}, s_{l_i + 1}, \ldots, s_{r_i}])$ , answer to the $i$ -th query.