Which of the following algorithms has better computational complexity than standard division algorithms?

Which of the following algorithms has better computational complexity than standard division algorithms? Correct Answer Classical modular exponentiation algorithm

To multiply m and n, they are converted to Montgomery form: mR mod X and nR mod X. When multiplied, these produce mnR2 mod X, and the Montgomery reduction produces abR mod N which is the Montgomery form of the desired product. After that, the low bits are discarded which gives a result less than 2X. One final subtraction reduces this to less than X. Hence, this procedure can have a better computational complexity than standard division algorithms.