Dynamic Programming – Maximum Product Cutting Problem.

Objective: Given a rope of length n meters, write an algorithm to cut the rope in such a way that the product of different lengths of rope is maximum. At least one cut has to be made.

Note: Assume that the length of the rope is more than 2 meters since at least one cut has to be made.

This is yet another problem where you will see the advantage of dynamic programming over recursion. I will show you how storing and reusing the results of sub-problems will reduce the complexity of an algorithm significantly. This kind of questions is asked in interviews like Amazon, Microsoft, Google, etc.

Example:

•	Rope length: 2 
•	Options: (1*1)
•	Maximum Product Cutting : 1*1 = 1

•	Rope length: 3 
•	Options: (1*1*1, 2*1)
•	Maximum Product Cutting : 2*1 = 2

•	Rope length: 4 
•	Options: (1*1*1*1, 2*1*1, 3*1, 2*2)
•	Maximum Product Cutting : 2*2 = 4

•	Rope length: 5 
•	Options: (1*1*1*1*1, 2*1*1*1, 3*1*1, 2*2*1, 3*2)
•	Maximum Product Cutting : 3*2 = 6

Approach:

Using Recursion:

This problem is similar to the “Rod Cutting Problem“.

  • Check the products of all possible cuts that can be made in the rope and return the maximum product.
  • For every length, there are two options, either a cut to be made or not. Solve the problem for both options and choose the maximum.
  • After Making the cut the further options are, Either this cut will produce the max product OR we need to make further cuts

Recursive Equation:

Let MPC(n) is the maximum product for length n.

  • MPC(n) = max(i*(n-i), i*MPC(n-i)) for all (i=1,2…..n) (After Making the cut the further options are , Either this cut will produce the max product OR we need to make further cuts).
Maximum Product Cutting - Recursion

Time Complexity: O(2n).

Code:

But yet again we are solving many sub-problems repeatedly.

Dynamic Programming:

We will solve this problem in a Bottom-Up manner.

We will store the solutions for sub-problems when it getting solved for the first time and use them again in the future so that we don’t have to solve them again.
Time Complexity: O(N^2)
See the Code for a better understanding.

Code:

Output:

Dynamic Programming: Maximum product cutting in 10 is: 36