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

Grokking the Blind 75 Problems in Go

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

# Statement
Given an unsigned 32-bit integer `n`, we need to calculate a 32-bit unsigned integer with reversed bits. When we say “reverse” we don’t mean flipping the $0$s to $1$s and vice versa, but simply reversing the order in which they appear, i.e., from left-to-right to right-to-left.

**Constraints:**

* The input must be a binary string of length $32$

# Examples


What is the output if we have 5 as an unsigned 32-bit integer and reverse the bits?

What is the output if we have 5 as an unsigned 32-bit integer and reverse the bits?

What is the output if we have 41596 as an unsigned 32-bit integer and reverse the bits?

What is the output if we have 41596 as an unsigned 32-bit integer and reverse the bits?

Reverse Bits

Reverse Bits

## 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.

> **Note:** As an additional challenge, we have intentionally hidden the solution to this puzzle. 

package main

func reverseBits(n uint32) uint32 {

    // Replace this placeholder return statement with your code
	return 0
}

# 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: `revbits`\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 `revbits` 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 `revbits`.\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) `revbits`. \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) `revbits`. \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.

INTEGER

package main

import (
	"fmt"
	"os"
	"strconv"
	"encoding/json"

)


type INTEGER struct {
	// class attributes
	res uint32
}

func (ds *INTEGER) generateError(data string) {
	fmt.Fprintln(os.Stderr, "Parsing Error: ", data, " in INTEGER is not parsable")
	os.Exit(-1)
}

func (ds *INTEGER) String() string {
	// override print() for your data structure
	return ""
}

// return value will be passed to user program
func (ds *INTEGER) Construct(value string, type_of_arr int) any {
	// parse test case in json string 'value' to your desired data structure
    json.Unmarshal([]byte(value), &ds.res)
    return *ds
}

// input param contains return value of user program
func (ds *INTEGER) Traverse(input any, type_of_arr int) string {
	// convert your data structure 'input' to a json string representing a test case output
	return strconv.Itoa(int(input.(INTEGER).res))
}


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 reverse_bits(n):
 n = (n >> 16) | (n << 16)
 n = ((n & 0xff00ff00) >> 8) | ((n & 0x00ff00ff) << 8)
 n = ((n & 0xf0f0f0f0) >> 4) | ((n & 0x0f0f0f0f) << 4)
 n = ((n & 0xcccccccc) >> 2) | ((n & 0x33333333) << 2)
 n = ((n & 0xaaaaaaaa) >> 1) | ((n & 0x55555555) << 1)
 return n
 
 expected1 = reverse_bits(binary_to_decimal(self.__inputs[0]))
 expected = str(expected1) + " ("+ str(decimal_to_32bit_binary(expected1))+ ")"
 actual = str(self.__actual_outputs[0])
 # multiple outputs will be added at each index respectively for a single test_case
 expected_outputs = [] 
 # store the 1st expected output that should be displayed to the user 
 expected_outputs.append(expected)
 if expected == actual:
 self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
 else:
 self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)

 return self.__edu_result

def decimal_to_32bit_binary(decimal_number):
 # Special case for zero
 if decimal_number == 0:
 return "0" * 32
 
 binary_str = ""
 
 # Loop until the decimal number is greater than 0
 while decimal_number > 0:
 # Get the remainder of the division by 2 (0 or 1)
 remainder = decimal_number % 2
 # Add the remainder to the binary string
 binary_str = str(remainder) + binary_str
 # Update the decimal number to be the quotient of the division by 2
 decimal_number = decimal_number // 2
 
 # Ensure the binary string is 32 bits long by padding with leading zeros
 binary_str = binary_str.zfill(32)
 
 return binary_str

def binary_to_decimal(binary_str):
 # Initialize the decimal value
 decimal_value = 0
 
 # Reverse the binary string to process from the least significant bit
 binary_str_reversed = binary_str[::-1]
 
 # Iterate over the binary string
 for i in range(len(binary_str_reversed)):
 # Add the value of the current bit to the decimal value
 decimal_value += int(binary_str_reversed[i]) * (2 ** i)
 
 return decimal_value

package main


import (
	"fmt"
	"strings"
)

// Function to convert a binary string to a decimal number
func binaryToDecimal(binaryStr string) uint32 {
	var decimalValue uint32 = 0

	// Reverse the binary string to process from the least significant bit
	reversed := reverseString(binaryStr)

	// Iterate over the binary string
	for i := 0; i < len(reversed); i++ {
		// Convert the character to an integer (0 or 1)
		bit := uint32(reversed[i] - '0')
		// Add the value of the current bit to the decimal value
		decimalValue += bit <= 0; i-- {
		sb.WriteByte(s[i])
	}
	return sb.String()
}

// Function to convert a decimal number to a 32-bit binary string
func decimalTo32bitBinary(decimalNumber uint32) string {
	if decimalNumber == 0 {
		return "00000000000000000000000000000000"
	}

	var binaryStr strings.Builder

	// Loop until the decimal number is greater than 0
	for decimalNumber > 0 {
		// Get the least significant bit (remainder of division by 2)
		remainder := decimalNumber % 2
		// Convert remainder to character ('0' or '1') and prepend to binaryStr
		binaryStr.WriteByte(byte('0' + remainder))
		// Update decimalNumber to the quotient of the division by 2
		decimalNumber = decimalNumber >> 1 // Shift right is equivalent to division by 2
	}

	// Ensure the binary string is 32 bits long by padding with leading zeros
	for binaryStr.Len() < 32 {
		binaryStr.WriteByte('0')
	}

	// Reverse the completed binary string before returning
	return reverseString(binaryStr.String())
}

// Main function to convert binary string to decimal, reverse bits, and convert back to binary string
func revbits(n string) string {
	n1 := binaryToDecimal(n)
	res := reverseBits(n1)
	return fmt.Sprintf("%d (%s)", res, decimalTo32bitBinary(res))
}

reverse_bits.yaml

testcases:
  - name: "Test Case 1 (Generate All Bits One)"
    inputs:
      - 1:  "11111111111111111111111111111111"
    output:
      - 1: 4294967295 (11111111111111111111111111111111)
  - name: "Test Case 2 (Generate Single Bit Set At Start)"
    inputs:
      - 1:  "00000000000000000000000000000001"
    output:
      - 1: 2147483648 (10000000000000000000000000000000)
  - name: "Test Case 3 (Generate Single Bit Set At End)"
    inputs:
      - 1:  "10000000000000000000000000000000"
    output:
      - 1: 1 (00000000000000000000000000000001)
  - name: "Test Case 4 (Generate Single Bit Set At Random Position)"
    inputs:
      - 1:  "00001000000000000000000000000000"
    output:
      - 1: 16 (00000000000000000000000000010000)
  - name: "Test Case 5 (Generate Alternating Bits)"
    inputs:
      - 1:  "10101010101010101010101010101010"
    output:
      - 1: 1431655765 (01010101010101010101010101010101)

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
        """
        # inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 1
        if len(self.__inputs[0]) != 32:
            self.store_result ("The input must be a binary string of length 32", ValidationFunction.FAIL)
        elif not(is_binary_string(self.__inputs[0])):
            self.store_result ("The input must be a binary string", ValidationFunction.FAIL)
        else:
            self.store_result("", ValidationFunction.PASS)

def is_binary_string(s):
    """
    Checks whether the given string is a binary string.

    Args:
    s (str): The string to check.

    Returns:
    bool: True if the string is binary, False otherwise.
    """
    # Iterate over each character in the string
    for char in s:
        # If the character is not '0' or '1', return False
        if char not in {'0', '1'}:
            return False
    # If all characters are '0' or '1', return True
    return True


Bitwise Manipulation

Sliding Window

Union Find

Conclusion

Reverse Bits

Statement

Examples

Understand the problem

Figure it out!

Try it yourself