variable A , B , AB for count strings that end with ' A ' but not end with ' B ' , ' B ' but does not end with ' A ' and ' B ' and ends with ' A ' respectively .
var A = 0 , B = 0 , BA = 0 , ans = 0 ; for ( var i = 0 ; i < n ; i ++ ) { var S = s [ i ] ; var L = S . length ; for ( var j = 0 ; j < L - 1 ; j ++ ) {