Problem:
Score : 300 points

Problem Statement

You are given a string S of length N consisting of A, C, G and T. Answer the following Q queries:

Query i (1 \leq i \leq Q): You will be given integers l_i and r_i (1 \leq l_i < r_i \leq N). Consider the substring of S starting at index l_i and ending at index r_i (both inclusive). In this string, how many times does AC occurs as a substring?

Notes

A substring of a string T is a string obtained by removing zero or more characters from the beginning and the end of T.

For example, the substrings of ATCODER include TCO, AT, CODER, ATCODER and (the empty string), but not AC.

Constraints

2 \leq N \leq 10^5

1 \leq Q \leq 10^5

S is a string of length N.

Each character in S is A, C, G or T.

1 \leq l_i < r_i \leq N

Input

Input is given from Standard Input in the following format:

N Q
S
l_1 r_1
:
l_Q r_Q

Output

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

Sample Input 1

8 3
ACACTACG
3 7
2 3
1 8

Sample Output 1

2
0
3

Query 1: the substring of S starting at index 3 and ending at index 7 is ACTAC. In this string, AC occurs twice as a substring.

Query 2: the substring of S starting at index 2 and ending at index 3 is CA. In this string, AC occurs zero times as a substring.

Query 3: the substring of S starting at index 1 and ending at index 8 is ACACTACG. In this string, AC occurs three times as a substring.

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Control.Monad
import qualified Data.ByteString.Char8 as BC
import Data.Maybe
import qualified Data.IntMap as IntMap

type Map = IntMap.IntMap Int

readIntsLine :: IO [Int]
readIntsLine = map (fst . fromJust . BC.readInt) . BC.words <$> BC.getLine

solve :: String -> String -> Int -> Int -> Map -> Map
solve [] _ _ _ m = m
solve (s:ss) prev step count m = solve ss [s] (step + 1) nextcount nextmap
  where nextcount = if prev ++ [s] == "AC" then count + 1 else count
        nextmap = IntMap.insert step nextcount m

main :: IO ()
main = do
  [n, q] <- map read . words <$> getLine
  s <- getLine
  let m = solve s "" 1 0 IntMap.empty
  replicateM_ q $ do
    [l, r] <- readIntsLine
    let lcount = fromMaybe 0 $ IntMap.lookup l m
    let rcount = fromMaybe 0 $ IntMap.lookup r m
    print $ rcount - lcount