You have n coins, labeled 0 through n-1.
Each of the coins shows either heads or tails.
You are given the states of all coins in the String state with n characters.
For each i, state[i] is 'H' if coin i shows heads, or 'T' if it shows tails.
The coins are laid out in a row, ordered from coin 0 to coin n-1.
A coin is called interesting if it differs from at least one of its neighbors.
(For example, a coin that shows heads is interesting if at least one of its neighbors shows tails.)
Return the number of interesting coins.