First I tried to solve by creating an isPrime boolean function which would check if each index is prime or not. Then I ran a loop for all indices and calculated the sum. This gave TLE. Then I created a boolean array to keep a track of all the prime elements and applied the Sieve of Eratosthenes method to calculate the prime indices and then compute the result.

Tried a basic approach to a two-pass solution. First calculated left sum starting from index 0 to index mid. Then calculated the right sum in a similar fashion from the last index to mid+1. Optimized the code using 2 pointer technique.

They asked me the approach. I did it just as I learned on Coding Ninjas. Create a path from the root to the node. Create a recursive function to find descendant at distance k below from a given node. Use this function for all elements in the path you found out.