Problem link: https://www.hackerrank.com/challenges/manasa-and-stones
Manasa is out on a hike with friends. She finds a trail of stones with numbers on them. She starts following the trail and notices that two consecutive stones have a difference of either
Note: The numbers on the stones are in increasing order.
Analysis: On this problem the questioner is asking for the possible combination of addition of a and b integer in an increasing series and the last number of the series. As it is an increasing series then it is must that either a or b will be added to the next number of the series. So possible combination for the n stone with 2 number (a and b) is 2^n number of solution. But as start stone is always 0, then you have 2^n-1 place. Now as your set consist of just 2 number you can get the number of solution by just increasing occurrence of a and decreasing the number of occurrence b. So at the end last number of the series is,
last num = a*num-occurrence + b * num-occurence
So for n number of places iterate this equation for the all possible solution,
last num = a*n + b*(max_place - 1 - n) //Where max_place is number of stone
N.B. Consider corner cases on input which is not added on the solution analysis.