Learn and practice the Bitwise Manipulation, Sliding Window, and Union Find patterns to solve coding interview problems.

Educative-77 in Go: Accelerate Your Coding Interview Prep

Each of the patterns in this module exemplifies the power of dissecting a problem in detail and figuring out the least expensive operations required to solve it. In the Bitwise Manipulation pattern, we’ll learn to leverage the power of bit-level operators to deliver more efficient solutions. With the Sliding Window pattern, we’ll gain practice in various techniques to ensure that a solution that seems to require nested loops actually executes in linear time. Using the Union Find pattern, we’ll learn to solve a diverse set of problems using the disjoint-set data structure.

Elegant by Design

# Understand the problem

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



(**Select all that apply.**) What is the output if the following array is given as an input?

arr = [1, 6, 2, 1, 2, 4, 7, 4]



(Select all that apply.) What is the output if the following array is given as an input?
arr = [1, 6, 2, 1, 2, 4, 7, 4]

(**Select all that apply.**) What is the output if the following array is given as an input?

arr = [-1, -6, 2, 1, 2, 4, 7, 4, 1, 7]

**Select all that apply.**

(Select all that apply.) What is the output if the following array is given as an input?
arr = [-1, -6, 2, 1, 2, 4, 7, 4, 1, 7]
Select all that apply.

What is the output if the following array is given as an input?

arr = [0, 1, 2, 3, 0, 1, 2, 3, 4, 5]


What is the output if the following array is given as an input?
arr = [0, 1, 2, 3, 0, 1, 2, 3, 4, 5]

Two Single Numbers

Two Single Numbers

# 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.

# Try it yourself

Implement your solution in the following coding playground:

# 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: `twoSingleNumbers`\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 `twoSingleNumbers` 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 `twoSingleNumbers`.\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) `twoSingleNumbers`. \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) `twoSingleNumbers`. \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
        """
        def two_single_numbers_test(arr):
            bitwise_sum = 0
            for i in arr:
                bitwise_sum ^= i

            # the least significant bit can be found with number ^ (-number)
            bitwise_mask = bitwise_sum & (-bitwise_sum)

            # divide into two groups of numbers, here we want the group with bit set
            # which results in one of the numbers we want due to the property X ^ X = 0
            results = 0
            for i in arr:
                if bitwise_mask & i:
                    results = results ^ i

            return [results, bitwise_sum ^ results]
        
        expected = two_single_numbers_test(self.__inputs[0])
        actual = self.__actual_outputs[0]
        # multiple outputs will be added at each index respectively for a single test_case
        expected_outputs = [] 

        if actual == None:
            expected_outputs.append(expected)
            self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)  
        elif expected == actual:
            expected_outputs.append(expected) 
            self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)      
        elif actual != expected:
            if sorted(actual) == sorted(expected):
                expected_outputs.append(actual)
                self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
            else: 
                expected_outputs.append(expected)
                self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)
        else: 
            expected_outputs.append(expected)
            self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)  

        return self.__edu_result

package main

func twoSingleNumbers(arr []int) []int {

    // Replace this placeholder return statement with your code
    return make([]int, 0)
}

two_single_numbers.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : [1, 2, 2, 3, 3, 4]
    output: 
    - 1 : [1, 4]
  - name: "testcase 2"
    inputs:
    - 1: [2, 1, 1, 8]
    output:
    - 1 : [2, 8]
  - name: "testcase 3"
    inputs:
    - 1:  [4, 1, 2, 1, 2, 0]
    output:
    - 1: [0, 4]
  - name: "testcase 4"
    inputs:
    - 1: [2, 5]
    output:
    - 1: [2, 5]
  - name: "testcase 5"
    inputs:
    - 1: [4, 5, 4, 1, 1, 2, 6, 6]
    output:
    - 1: [5, 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)
 # inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 1
 def is_twice_except_two(arr):
 element_count = {}
 unique_set = set()

 for num in arr:
 if num in element_count:
 element_count[num] += 1
 else:
 element_count[num] = 1
 unique_set.add(num)

 single_occurrence_count = 0

 for count in element_count.values():
 if count == 1:
 single_occurrence_count += 1
 elif count != 2:
 return False # Element appears more than twice

 return single_occurrence_count == 2

 nums = self.__inputs[0]
 # inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 1
 if not is_valid_1d_array(nums):
 self.store_result(("Invalid test case."), ValidationFunction.FAIL) 
 
 elif not (2<= len(nums) <= 1000):
 self.store_result(("The number of values in the array should be in the range [2, 1000] but got " + str(len(nums)) + "."), ValidationFunction.FAIL)

 elif not (is_twice_except_two(nums)):
 self.store_result ("Invalid test case.", ValidationFunction.FAIL)
 
 elif not all(-2**31 <= num <= (2**31)-1 for num in nums):
 self.store_result ("`nums` must consist of values from -2^31 to 2^31-1 only", ValidationFunction.FAIL)
 
 else:
 self.store_result("", ValidationFunction.PASS)

Try to solve the Single Number II problem.


Single Number II

Try to solve the Single Number II problem.

Bitwise Manipulation

Sliding Window

Union Find

Conclusion

Two Single Numbers

Statement

Examples

Understand the problem

Figure it out!

Try it yourself