Let abcd be 4 digit number, such that we can do transformations on it. If some two neighboring digits are different than 0, then we can decrease both digits by 1 (we can transform 9870 to 8770 or 9760). If some two neighboring digits are different than 9, then we can increase both digits by 1 (we can transform 9870 to 9980 or 9881). Can we transform number 1220 to:
a) 2012
b) 2021 combinatoricstransformationsDigits