Given an integer N, the task is to find the minimum number of steps to reach the number N from 1 by multiplying each step by 2, 3, 4 or 5. If it is not possible to reach N, print -1.
Input: N = 10
Initial number = 1
Step 1: Multiply it by 2, Current Number = 2
Step 2: Multiply it by 5, Current Number = 10
Therefore, Minimum 2 steps required to reach 10.
Input: N = 13
There is no way reach 13 using any given operations
Approach: The idea is to use Greedy Alogorithm to choose the operation that should be performed at each step and perform the operations in the reverse manner that is instead of going from 1 to N, find the operations required to reach N to 1. Below is the illustration of the steps:
- Apply the operations below until N is greater than 1.
- Check if N is divisible by 5, Then increase steps by 1 and reduce N to N/5
- Else, check if N is divisible by 4, Then increase steps by 1 and reduce N to N/4
- Else, check if N is divisible by 3, Then increase steps by 1 and reduce N to N/3
- Else, check if N is divisible by 2, Then increase steps by 1, and reduce N to N/2
- If at any step no operation can be applied then there is no possible set of operations to reach N from 1. Therefore, return -1.
Below is the implementation of the above approach:
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