### rprudhvi590's blog

By rprudhvi590, history, 9 months ago,
• Given an integer n, find and return the n'th magic number
• A magic number is defined as a number which can be expressed as a power of 7 or sum of unique powers of 7
• First four magic numbers are  7 ,  49 ,  56 (7 + 49),  343,etc . constraint 1<=n<=pow(10,18) i have implemented the solution as follows:

https://ideone.com/Q8OM0b but it gives me wrong answer,the only difference is that when calculating the value of add we need to apply mod;and the solution is as follows:

https://ideone.com/k1KhFA

how will we know where to apply a mod operator..pls help.

• 0

 » 9 months ago, # |   0 its better to apply after every operation. say, a + b * c, do it like (a + (b*c) % mod ) % mod also take care of case of int overflow, either use long long or while(x < 0) x = x + mod.
•  » » 9 months ago, # ^ |   0 it didnt work even after applying after every operation.the solution says that we need to apply mod while calculating the power of 7.
•  » » » 9 months ago, # ^ |   0 then ur implementation is wrong. check it from here.. https://www.google.com/amp/s/www.geeksforgeeks.org/find-nth-magic-number/amp/
 » 9 months ago, # |   0 Auto comment: topic has been updated by rprudhvi590 (previous revision, new revision, compare).
 » 9 months ago, # |   0 Auto comment: topic has been updated by rprudhvi590 (previous revision, new revision, compare).