question: public String mutateLangModel ( final String input ) { if ( input . length ( ) == 0 ) { return input ; } int startPoint = ( int ) ( Randomness . nextDouble ( ) * ( input . length ( ) ) ) ; int remainingLength = ( int ) Math . round ( Randomness . nextDouble ( ) * ( input . length ( ) - startPoint ) ) ; if ( remainingLength == 0 ) { return input ; } String output = input . substring ( 0 , startPoint ) ; String replacementChunk = generateRandomStringFromModelWithExactLength ( remainingLength , "" + input . charAt ( startPoint ) ) ; output += replacementChunk ; output += input . substring ( startPoint + remainingLength , input . length ( ) ) ; return output ; }
target:  Produce a new string similar to input. Selects a random substring of the string and for each character in that substring: gets the character preceeding it gets a character the language model predicts to follow that prefix replaces the character with the predicted character