Learn and practice the In-place Reversal of a Linked List, Stacks, and Matrices patterns to solve coding interview problems.

Educative-77 in Go: Accelerate Your Coding Interview Prep

Interviewers want to be sure that the candidate is comfortable manipulating linked lists, arrays, and data structures based on them, such as stacks and matrices. This module will provide the practice you need to review the concepts and techniques needed to solve common problems involving these data structures.

Basic Data Structures

## Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps us to check if you’re solving the correct problem:


3 → 4 → 2 → 1 → 5 → 0 → 7 → 8 → 6

3 → 4 → 5 → 0 → 2 → 1 → 8 → 7 → 6

4 → 0 → 3 → 5 → 1 → 2 → 8 → 7 → 6

4 → 0 → 3 → 5 → 1 → 2 → 7 → 8 → 6

What is the output if the following linked list is provided as input?

4 → 3 → 0 → 5 → 1 → 2 → 7 → 8 → 6

What is the output if the following linked list is provided as input?
4 → 3 → 0 → 5 → 1 → 2 → 7 → 8 → 6

What is the output if the following linked list is provided as input?

1 → 0 → 2



What is the output if the following linked list is provided as input?
1 → 0 → 2

13 → 8 → 3 → 9 → 2 → 12 → 4 → 7 → 1 → 6 → 0 → 11 → 6 → 14 → 10

8 → 9 → 13 → 3 → 12 → 2 → 1 → 5 → 4 → 7 → 11 → 0 → 14 → 10 → 6


8 → 9 → 13 → 3 → 12 → 2 → 1 → 5 → 4 → 7 → 11 → 0 → 14 → 6 → 10

13 → 8 → 9 → 3 → 12 → 5 → 4 → 7 → 2 → 1 → 11 → 0 → 14 → 6 → 10

What is the output if the following linked list is provided as input?

8 → 13 → 9 → 3 → 12 → 2 → 7 → 4 → 5 → 1 → 11 → 0 → 14 → 6 → 10


What is the output if the following linked list is provided as input?
8 → 13 → 9 → 3 → 12 → 2 → 7 → 4 → 5 → 1 → 11 → 0 → 14 → 6 → 10

Reverse Nodes in Even Length Groups

Reverse Nodes in Even Length Groups

## Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

package main
import (. "golang-test-code/ds_v1/LinkedList")

func driverCode(input1 *ListNode) *ListNode {
    
    reverseEvenLengthGroups(input1)
    
    return input1
}

# Quick Fix\nYou are Edward, a Senior Software Engineer who specializes in coding interview patterns, data structures and algorithms, and is great at debugging issues in code.\n\n- Edward, please keep in mind that you do not have to print the data of the placeholders. Also, do not mention anything about yourself.\n\nEdward, you are given the following data in the placeholders:\n- Function name: `reverseEvenLengthGroups`\n- Candidate's submitted solution code: USER_CODE\n- Error: ERROR_DESCRIPTION\n- Failed test case: FAILED_TEST_CASE\n- Coding language: `Go`\n\n- Edward, your task is to understand the type of error that is occurring in the coding language provided.\n- Once you've understood the error as per the error’s description, and why the test case failed, you will suggest how the candidate can improve their solution code to fix the error.\n- Edward, you will not give the corrected code, just a hint on what the error tells, and how to fix it.\n- Edward, please limit your response strictly to 100 words. No more words than the limit.

# Review Code\nEdward, your current task is to review the `reverseEvenLengthGroups` function(s) and the other function(s) invoked in it/them.\n\n-Take your time and review the candidate's solution code.\n- Do not review any extra/helper files or functions not invoked in the solution function `reverseEvenLengthGroups`.\n- Do not review the code of data structure objects instantiated like a binary tree, linked list, trie, union find, etc., in the solution functions. Just review the solution/algorithm function of the problem. \n- Also, if the solution code doesn’t use the coding pattern stated above, then please encourage the candidate to reattempt the problem using that pattern corectly.

# Review time complexity\n- Please provide a brief time complexity analysis of the function(s) `reverseEvenLengthGroups`. \n- While calculating time complexity, include the time complexity of built-in Go functions invoked by the code. \n- The answer should be to the point in approximately 60 words.

# Review space complexity\n- Please provide a brief space complexity analysis of the function(s) `reverseEvenLengthGroups`. \n- While calculating space complexity, include the space complexity of built-in Go functions invoked by the code. \n- Do not include the space used for the input parameters and the space used for just returning an output (not used as a scratch space). \n- The answer should be to the point in approximately 60 words.

def evaluate_results(self) -> object:
        """
        self.__inputs is the list of inputs that are passed as input to function
        self.__actual_output is a list of outputs that is produced by the learner's code
        return : self.__edu__result object
        """

        # Template for linked list node class

        class LinkedListNode:
            # __init__ will be used to make a LinkedListNode type object.
            def __init__(self, data, next=None):
                self.data = data
                self.next = next

        # Template for the linked list
        class LinkedList:
            # __init__ will be used to make a LinkedList type object.
            def __init__(self):
                self.head = None
            
            # insert_node_at_head method will insert a LinkedListNode at 
            # head of a linked list.
            def insert_node_at_head(self, node):
                if self.head:
                    node.next = self.head
                    self.head = node
                else:
                    self.head = node
            
            # create_linked_list method will create the linked list using the
            # given integer array with the help of InsertAthead method. 
            def create_linked_list(self, lst):
                for x in reversed(lst):
                    new_node = LinkedListNode(x)
                    self.insert_node_at_head(new_node)
            
            # __str__(self) method will display the elements of linked list.
            def __str__(self):
                result = ""
                temp = self.head
                while temp:
                    result += str(temp.data)
                    temp = temp.next
                    if temp:
                        result += ", "
                result += ""
                return result

        def reverse_even_length_groups(head):
            prev = head  
            l = 2

            while prev.next:
                node = prev
                n = 0
                for i in range(l):
                    if not node.next:
                        break
                    n += 1
                    node = node.next
                if n % 2:  
                    prev = node
                else:      
                    reverse = node.next
                    curr = prev.next
                    for j in range(n):
                        curr_next = curr.next
                        curr.next = reverse
                        reverse = curr
                        curr = curr_next
                    prev_next = prev.next
                    prev.next = node
                    prev = prev_next
                l += 1

            return head

        # multiple outputs will be added at each index respectively for a single test_case
        input_0 = LinkedList()
        input_0.create_linked_list(self.__inputs[0])
        expected = reverse_even_length_groups(input_0.head)

        actual = self.__actual_outputs[0]
        # print(actual)
        expected_list_values = []
        current_1 = expected
        while current_1:
            expected_list_values.append(current_1.data)
            current_1 = current_1.next

        
        actual_list_values = []

        expected_outputs = [] 
        expected_outputs.append(expected_list_values)
        if expected_list_values == actual:
            self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
        else:
            self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)

        return self.__edu_result

// Definition for a Linked List node

// type ListNode struct {
// 	Val  int
// 	Next *ListNode
// }

package main
import (. "golang-test-code/ds_v1/LinkedList")

func reverseEvenLengthGroups(head *ListNode) {
	
	// Replace this placeholder return statement with your code
}

reverse_nodes_in_even_length.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : [1, 2, 3, 4]
    output: 
    - 1 : [1, 3, 2, 4]
  - name: "testcase 2"
    inputs:
    - 1 : [10, 1, 2, 3, 4, 5]
    output: 
    - 1 : [10, 2, 1, 3, 4, 5]
  - name: "testcase 3"
    inputs:
    - 1 : [28, 21, 14, 7]
    output: 
    - 1 : [28, 14, 21, 7]
  - name: "testcase 4"
    inputs:
    - 1 : [11, 12, 13, 14, 15]
    output: 
    - 1 : [11, 13, 12, 15, 14]
  - name: "testcase 5"
    inputs:
    - 1 : [1, 2]
    output: 
    - 1 : [1, 2]

def sum(input_1, input_2):
    return input_1+input_2

def validate_inputs(self) -> None:
 """
 self.__inputs is the list of inputs that are passed as input to function
 store the result using the self.store_result(error_msg, status)
 return : void
 """
 def is_valid_1d_array(arr):
 if not isinstance(arr, list):
 return False # Not a valid 1D array if it's not a list
 
 return all(isinstance(elem, int) and not isinstance(elem, bool) for elem in arr)

 inp = self.__inputs[0]
 # inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 1
 if not is_valid_1d_array(inp):
 self.store_result(("Invalid test case."), ValidationFunction.FAIL) 
 elif not (1 <= len(inp) <= 500):
 self.store_result(("The number of nodes in the linked list should be in the range [1, 500] but got " + str(len(inp)) + "."), ValidationFunction.FAIL)
 elif not all(0 <= num <= 1000 for num in inp):
 self.store_result ("Linked list must consist of values from 0 to 1000 only", ValidationFunction.FAIL)
 else:
 self.store_result("", ValidationFunction.PASS)

Try to solve the Reverse Nodes in Even Length Groups problem.

In-Place Manipulation of a Linked List

Stacks

Matrices

Conclusion

Reverse Nodes In Even Length Groups

Statement

Examples

Understand the problem

Figure it out!

Try it yourself