Round 1: Coding Test, Hackerrank Platform, 3 questions, 1.5 hr
1. In a given array of length n, find max(A[j] – A[i]) such that i < j.
2. A person can create a flower bouquet with either 3 roses (cost of bouquet = p) or 1 rose and 1 lily (cost = q)
In an array of flowers, the person has to select contiguous set of flowers i.e. 2 or 3 to gain maximum cost.
Input format: A string of 0(denotes rose) and 1(denotes lily).
Output : Maximum cost.
Input: p = 2, q = 3, s = 0001000 Output: 5
Solution: Dynamic programming
if three consecutive 0's: dp[i] = max(dp[i-1], p + dp[i-3]) else if 1, 0 or 0, 1: dp[i] = max(dp[i-1], q + dp[i-2]) return dp[n-1]
Note: Handle the boundary values to avoid array index out of bound errors.
3. A graph is given in which nodes represent children and weighted edges join two children sharing a common hobby.
Example: If two nodes ‘i’ and ‘j’ are joined by an edge having value ‘k’, it means both ‘i’ and ‘j’ have a common interest ‘k’.
Find the maximal product of ‘i’, ‘j’, where ‘i’, ‘j’ are the children sharing maximum number of common hobbies.
Solution: Create a hash table storing the number of edges between a pair ‘i’, ‘j’. Find the max product of ‘i’ and ‘j’ if they have maximum number of edges between them.
Those who solved all three were selected for next round(27 students).
Round 1: Technical
1. In a given tree, find the maximum possible sum such that if a node is selected, it’s children can’t be selected i.e. if the value of node is added to the sum, it’s children can’t be present in the sum. I was asked to write the pseudocode in 5 mins(a timer was running).
Solution: Dynamic Programming on Trees
2. In a given array, find the longest subarray such that adjacent elements differ by one.
3. In a given array, find the longest subsequence such that adjacent elements differ by one.
4. Given a function f, such that f(x) = y such that 1 <= y <= x, create a random permutation of a given string. It should create random permutations every time.
Solution: Swap str[n-i] and str[f(n-i)] where i varies from 1 to n.
Round 2: Technical
1. Create a chain with given set of strings such that in adjacent strings, last letter of first string = first letter of second string.
Input: tap cat pac Output: tap -> pac -> cat
It is known that it will form a cycle i.e. first letter of first string of the chain = last letter of last string of the chain.
Solution: Chain array of strings to form a circle
I gave a solution using one hash table and one array, which was basically a DFS traversal. The interviewer hadn’t seen this approach and gave a lot of test cases, which passed.
2. Given n players and result of the matches held them, create a string such that, if A defeated B and B defeated C, then they should be placed as ABC. It is possible that C has defeated A.
Similar to the previous question. He wanted the solution involving directed graph and backtracking, so he asked this question.
3. Puzzle: Player 1 and Player 2 take turns and place a coin on a circular disc. The last person who is able to place a coin on the disc wins. Devise a strategy such that Player 1(first person to place a coin) always wins.
Solution: Round Table Coin Game
4. Given a binary tree, print it’s left view. Write the pseudocode.
Input: 1 / \ 2 6 / \ 7 0 /\ / 3 9 2 Output: 1 2 7 3
Solution: Left view of Binary Tree
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