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
Create a method, `encode`, that converts an array of strings into a single string and then sends it over the network. Create another method, `decode`, that takes the encoded string and converts it back into the original array of strings.

**Constraints:**
- $1 \leq$ `strings.length` $\leq 100$
- $0 \leq$ `strings[i].length` $\leq 100$
- `strings[i]` consist of any possible combinations of characters from 256 valid ASCII characters.

# Examples

# 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:

What will be the input data type of the `encode` function?


What will be the input data type of the <code>encode</code> function?

What will be the output data type of the `encode` function?

What will be the output data type of the <code>encode</code> function?

What will be the input data type of the `decode` function?

What will be the input data type of the <code>decode</code> function?

What will be the output data type of the `decode` function?

What will be the output data type of the <code>decode</code> function?

Encode and Decode Strings

Encode and Decode Strings

# 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.

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

std::string encode(const std::vector<std::string>& strings) {
 
 // Replace this placeholder return statement with your code

 std::string encodedString;
 return encodedString;
}

std::vector<std::string> decode(const std::string& str) {
 
 // Replace this placeholder return statement with your code

 std::vector<std::string> decodedStrings;
 return decodedStrings;
}

package main

import (
	"bytes"
)

func encode(strings []string) string {

	// Replace this placeholder return statement with your code

	var encodedString bytes.Buffer
	return encodedString.String()
}

func decode(str string) []string {

	// Replace this placeholder return statement with your code

	var decodedString []string
	return decodedString
}

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class EncodeDecode {
 public static String encode(List<String> strings) {

 // Replace this placeholder return statement with your code

 StringBuilder encodedString = new StringBuilder();
 return encodedString.toString();
 }

 public static List<String> decode(String str) {

 // Replace this placeholder return statement with your code

 List<String> decodedString = new ArrayList<>();
 return decodedString;
 }
}

export function encode(strings) {

    // Replace this placeholder return statement with your code

    return ""
}

export function decode(string) {

    // Replace this placeholder return statement with your code

    return []
}

# 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: `encode, decode`\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 `encode, decode` 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 `encode, decode`.\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) `encode, decode`. \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) `encode, decode`. \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 encode2(strings):
 encoded_string = ""

 for x in strings:
 encoded_string += length_to_bytes(x) + x

 return encoded_string


 def decode2(string):
 i = 0
 decoded_string = []

 while i < len(string):
 length = bytes_to_length(string[i : i + 4])
 i += 4
 decoded_string.append(string[i : i + length])
 i += length

 return decoded_string


 def length_to_bytes(x):
 length = len(x) 
 bytes = []

 for i in range(4):
 bytes.append(chr(length >> (i * 8)))

 bytes.reverse()
 bytes_string = "".join(bytes)

 return bytes_string


 def bytes_to_length(bytes_string):
 result = 0

 for c in bytes_string:
 result = result * 256 + ord(c)

 return result
 
 def compareResult(expected, actual_output):
 
 if expected == actual_output:
 return True
 return False

 # 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 
 encoded_string = encode2(self.__inputs[0])
 expected = decode2(encoded_string)
 expected_outputs.append(expected)

 actual_output = self.__actual_outputs[0]
 compare = compareResult(expected, actual_output)
 if compare:
 self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
 else:
 self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)

 return self.__edu_result

#include "EncodeDecode.cpp"

std::vector<std::string> main1(const std::vector<std::string>& strings)
{
 std::string encoded = encode(strings);
 std::vector<std::string> decoded = decode(encoded);
 return decoded;
}

package main

func main1(a []string) []string {
	return decode(encode(a))
}

import java.util.*;

public class Main{
 public static List<String> main1 (List<String> strings) {
 String encoded = EncodeDecode.encode(strings);
 return EncodeDecode.decode(encoded);
 }
}

import {encode, decode} from './EncodeDecode.js';

export function main1(strings) {
  var encodedString = encode(strings);
  var decodedString = decode(encodedString);
  return decodedString;
}

encode and decode strings.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : ["I", "love", "educative"]
    output: 
    - 1 : ["I", "love", "educative"]
  - name: "testcase 2"
    inputs:
    - 1 : ["6^Hello_5","5_World^6"]
    output: 
    - 1 : ["6^Hello_5","5_World^6"]
  - name: "testcase 3"
    inputs:
    - 1 : ["I","love","programming"]
    output: 
    - 1 : ["I","love","programming"]
  - name: "testcase 4"
    inputs:
    - 1 : ["a", "b", "c", "d"]
    output: 
    - 1 : ["a", "b", "c", "d"]
  - name: "testcase 5"
    inputs:
    - 1 : ["coding", "is", "fun"]
    output: 
    - 1 : ["coding", "is", "fun"]

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
 """
 strings = self.__inputs[0]

 # inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 1
 if len(self.__inputs[0]) < 1 or len(self.__inputs[0]) > 100:
 self.store_result ("expected 'strings' to have " + str(1) + " <= size <= " + str(100) + " but got " + str(len(strings)), ValidationFunction.FAIL)

 elif any(len(x) < 0 or len(x) > 100 for x in self.__inputs[0]):
 self.store_result("expected rows of 'strings' to have " + str(0) + " <= size <= " + str(100), ValidationFunction.FAIL)

 elif any(any(ord(ch) not in range(256) for ch in s) for s in self.__inputs[0]):
 self.store_result("'strings[i]' should contain valid ASCII characters", ValidationFunction.FAIL)
 
 else:
 self.store_result("", ValidationFunction.PASS)

Try to solve the Encode and Decode Strings problem.

Bitwise Manipulation

Sliding Window

Union Find

Conclusion

Encode and Decode Strings

Statement

Examples

Understand the problem

Figure it out!

Try it yourself