Hike Software Developer Intern Interview Questions, Process, and Tips

Round duration - 90 minutes
Round difficulty - Medium

Timing was 10AM. The platform was quite good.

Q1. 
Maximum Size Rectangle Sub-matrix with All 1's Problem Statement
You are provided with an N * M sized binary matrix 'MAT' where 'N' denotes the number of rows and 'M' denotes the number of columns. Your t...read more
Ans. Dynamic Programming.
1. We start from the first row and move downwards.
2. We create three 1-dimensional arrays HEIGHT[], LEFT[], RIGHT[].
3. ‘HEIGHT’[i]: stores the number of current continuous 1’s in column i.
4. LEFT[i] : stores the leftmost index ‘j’ such that all indices say ‘K’, ‘K’ belongs to [j, i], ‘HEIGHT’[k] >= ‘HEIGHT’[i].
5. RIGHT [i]: stores the rightmost index ‘j’ such that all indices say ‘K’, ‘K’ belongs to [i, j], ‘HE...read more
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Q2. 
Binary Tree Maximum Path Sum Problem Statement
Determine the maximum path sum for any path in a given binary tree with 'N' nodes.
Note:
• A 'path' is defined as any sequence of adjacent nodes connected...read more
Ans. Recursive Approach
The idea here is to use the recursion. For each node, We can calculate the maximum path sum by keeping track of the following paths:
• Max path sum starting from Left child + Max Path sum starting from Right child + Node’s value.
• Max path sum starting from Left child + Node’s value
• Max path sum starting from Right child + Node’s value
• Node’s value
 
We then pick the maximum one among them. The root of ev...read more
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Q3. 
Minimum Number of Swaps to Sort an Array
Find the minimum number of swaps required to sort a given array of distinct elements in ascending order.
Input:
T (number of test cases)
For each test case:
N (siz...read more
Ans. Naive Approach
While iterating over the array, check the current element, and if not in the correct place, replace that element with the index of the element which should have come in this place.
 
Below is the algorithm:
1. Create a copy of the given input array and store it in temp.
2. Sort the temp array.
3. Iterate over the input array, and check whether the current element is at the right place or not by comparing it with t...read more
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Q4. 
Infix to Postfix Conversion
Convert a given infix expression, represented as a string EXP, into its equivalent postfix expression.
Explanation:
An infix expression is formatted as a op b where the opera...read more
Ans. Stack
We will scan the expression from left to write and if we encounter an operand we will append it to our answer. If we encounter an operator we will pop all the operators with equal or higher precedence and append them to our answer. And push the current operator. In the end, we will empty the stack.
Order of precedence = [ ‘^’, ‘*’ and ‘/’, ‘+’ and ‘-’, ‘(’, ‘)’]
Order of precedence [ link ]
The algorithm will be-
1. ANS ...read more
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Round duration - 90 minutes
Round difficulty - Medium

Timing was 10AM. The platform was user-friendly.

Q1. 
Maximum Size Rectangle Sub-matrix with All 1's Problem Statement
You are provided with an N * M sized binary matrix 'MAT' where 'N' denotes the number of rows and 'M' denotes the number of columns. Your t...read more
Ans. Dynamic Programming.
1. We start from the first row and move downwards.
2. We create three 1-dimensional arrays HEIGHT[], LEFT[], RIGHT[].
3. ‘HEIGHT’[i]: stores the number of current continuous 1’s in column i.
4. LEFT[i] : stores the leftmost index ‘j’ such that all indices say ‘K’, ‘K’ belongs to [j, i], ‘HEIGHT’[k] >= ‘HEIGHT’[i].
5. RIGHT [i]: stores the rightmost index ‘j’ such that all indices say ‘K’, ‘K’ belongs to [i, j], ‘HE...read more
Answered Anonymously
Add your answer
Q2. 
Binary Tree Maximum Path Sum Problem Statement
Determine the maximum path sum for any path in a given binary tree with 'N' nodes.
Note:
• A 'path' is defined as any sequence of adjacent nodes connected...read more
Ans. Recursive Approach
The idea here is to use the recursion. For each node, We can calculate the maximum path sum by keeping track of the following paths:
• Max path sum starting from Left child + Max Path sum starting from Right child + Node’s value.
• Max path sum starting from Left child + Node’s value
• Max path sum starting from Right child + Node’s value
• Node’s value
 
We then pick the maximum one among them. The root of ev...read more
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Add your answer
Q3. 
Minimum Number of Swaps to Sort an Array
Find the minimum number of swaps required to sort a given array of distinct elements in ascending order.
Input:
T (number of test cases)
For each test case:
N (siz...read more
Ans. Naive Approach
While iterating over the array, check the current element, and if not in the correct place, replace that element with the index of the element which should have come in this place.
 
Below is the algorithm:
1. Create a copy of the given input array and store it in temp.
2. Sort the temp array.
3. Iterate over the input array, and check whether the current element is at the right place or not by comparing it with t...read more
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Add your answer
Q4. 
Prefix to Infix Conversion
Transform a string representing a valid Prefix expression, which may contain operators '+', '-', '*', '/', and uppercase letters, into its corresponding Infix expression.
Examp...read more
Ans. Stack Based
The idea is to iterate over the expression from right to left and store the operands in a stack. Here, we are using a stack of strings for storing the operands. Whenever we encounter an operator, pop the top two operands from the stack and convert the expression to its infix form and then push back to the stack.
 
• Iterate from ‘i’ = |S| - 1 to 0. The idea behind this step is to store the operands.
  1. If the c...read more
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Round duration - 90 minutes
Round difficulty - Medium

Timing was 10AM. The platform was quite good.

Q1. 
Maximum Size Rectangle Sub-Matrix with All 1's
Given an N x M binary matrix 'MAT', where N is the number of rows and M is the number of columns, determine the maximum area of a submatrix consisting entire...read more
Ans. 
If the height of bars of the histogram is given then the largest area of the histogram can be found. This way in each row, the largest area of bars of the histogram can be found. To get the largest rectangle full of 1’s, update the next row with the previous row and find the largest area under the histogram, i.e. consider each 1’s as filled squares and 0’s with an empty square and consider each row as the base.
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Q2. 
Maximum Sum Path in a Binary Tree
Your task is to determine the maximum possible sum of a simple path between any two nodes (possibly the same) in a given binary tree of 'N' nodes with integer values.
Ex...read more
Ans. 
For each node there can be four ways that the max path goes through the node:
1. Node only
2. Max path through Left Child + Node
3. Max path through Right Child + Node
4. Max path through Left Child + Node + Max path through Right Child
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Q3. 
Minimum Number of Swaps to Sort an Array
Find the minimum number of swaps required to sort a given array of distinct elements in ascending order.
Input:
T (number of test cases)
For each test case:
N (siz...read more
Ans. 
This can be easily done by visualizing the problem as a graph. We will have n nodes and an edge directed from node i to node j if the element at i’th index must be present at j’th index in the sorted array.
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Q4. 
Prefix to Infix Conversion
Transform a string representing a valid Prefix expression, which may contain operators '+', '-', '*', '/', and uppercase letters, into its corresponding Infix expression.
Examp...read more
Ans. 
Algorithm for Prefix to Infix:

Read the Prefix expression in reverse order (from right to left)
If the symbol is an operand, then push it onto the Stack
If the symbol is an operator, then pop two operands from the Stack
Create a string by concatenating the two operands and the operator between them.
string = (operand1 + operator + operand2)
And push the resultant string back to Stack
Repeat the above steps until end of Prefix
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Round duration - 60 Minutes
Round difficulty - Easy

Q1. 
Maximum Difference in Matrix
Given an n x n matrix mat[n][n] of integers, find the maximum value of mat[c][d] - mat[a][b] for all possible indices where c > a and d > b.
Input:
The first line cont...read more
Ans. Brute Force
Recursively call the function and find the maximum number of the submatrix and update the answer for every element of the matrix.
 
Algorithm:-
1. Run a for loop from 0 to N-1  (Let’s say the iterator be i).
   1. Run a nested for loop from 0 to N-1 (Let’s say the iterator be j).
      1. Recursively find the answer of submatrix with top-left corner (i+1, j+1).
         1. If i+1== N or j+1== N return -infinity.
         2. Update answer as maxim...read more
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Round duration - 20 Minutes
Round difficulty - Easy