Learn and practice the Hash Maps and Knowing What to Track patterns to solve coding interview problems.

Educative-99 in Python: Accelerate Your Coding Interview Prep

Hash maps are powerful data structures that enable programmers to design more efficient solutions for certain problems. After practicing solving problems using hash maps, we will move to the more general problem-solving skill of figuring out the key characteristics of a problem, using various techniques to track them, in order to design remarkably efficient solutions for seemingly complex problems.

Hashing and Tracking

* Both the strings consist of valid ASCII characters.
* The length of the string is $0$ $\leq$ `length` $\leq$ $10^{4}$.

* The length of both strings is the same. 


## Understand the problem

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

What is the output, if the following strings are given as an input?

string1 = "ACAB"

string2 = "XCXY"


What is the output, if the following strings are given as an input?
string1 = “ACAB”
string2 = “XCXY”

What is the output, if the following strings are given as an input?

string1 = "aab"

string2 = "xyz"



What is the output, if the following strings are given as an input?
string1 = “aab”
string2 = “xyz”

What is the output, if the following strings are given as an input?

string1 = "awz"

string2 = "xwz"



What is the output, if the following strings are given as an input?
string1 = “awz”
string2 = “xwz”

What is the output, if the following strings are given as an input?

string1 = "AAAA"

string2 = "AAAA"



What is the output, if the following strings are given as an input?
string1 = “AAAA”
string2 = “AAAA”

Isomorphic strings

Isomorphic strings

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

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: `is_isomorphic`\n- Candidate's submitted solution code: USER_CODE\n- Error: ERROR_DESCRIPTION\n- Failed test case: FAILED_TEST_CASE\n- Coding language: `Python`\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 `is_isomorphic` 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 `is_isomorphic`.\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) `is_isomorphic`. \n- While calculating time complexity, include the time complexity of built-in Python 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) `is_isomorphic`. \n- While calculating space complexity, include the space complexity of built-in Python 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 is_isomorphic(string1, string2):
            map_str1_str2 = {}
            map_str2_str1 = {}

            for i in range(len(string1)):
                char1 = string1[i]
                char2 = string2[i]

                if char1 in map_str1_str2 and map_str1_str2[char1] != char2:
                    return False

                if char2 in map_str2_str1 and map_str2_str1[char2] != char1:
                    return False

                map_str1_str2[char1] = char2
                map_str2_str1[char2] = char1

            return True
        
        # Expected output
        expected = is_isomorphic(self.__inputs[0], self.__inputs[1])

        # Actual output
        actual = 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 json.dumps(expected) == json.dumps(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 is_isomorphic(string1, string2):
  
    # Replace this placeholder return statement with your code
    return False  


PrivateTestCases.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : egg
    - 2 : all
    output: 
    - 1 : True
  - name: "testcase 2"
    inputs:
    - 1: foo
    - 2: bar
    output:
    - 1 : False
  - name: "testcase 3"
    inputs:
    - 1: paper
    - 2: title
    output:
    - 1: True
  - name: "testcase 4"
    inputs:
    - 1: badc
    - 2: baba
    output:
    - 1: False
  - name: "testcase 5"
    inputs:
    - 1: aaeaa
    - 2: uuxyy
    output:
    - 1: False

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
 """
 import string
 
 def are_valid_characters(s):
 for char in s:
 if char not in string.printable:
 return False
 return True
 
 string1 = self.__inputs[0]
 string2 = self.__inputs[1]

 string1_length = len(string1)
 string2_length = len(string2)

 strings_lower_bound = 0
 strings_upper_bound = 5 * (10**4)
 
 # inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 1
 if not are_valid_characters(string1):
 self.store_result ("\"" + string1 + "\"" + " is not a valid value of type string", ValidationFunction.FAIL)

 elif not are_valid_characters(string2):
 self.store_result ("\"" + string2 + "\"" + " is not a valid value of type string", ValidationFunction.FAIL)

 elif string1_length > strings_upper_bound:
 self.store_result ("expected 'string1' to have " + str(strings_lower_bound) + " <= size <= " + str(strings_upper_bound) + " but got " + str(string1_length), ValidationFunction.FAIL)

 elif string1_length != string2_length:
 self.store_result("expected 'string2' to have " + str(string1_length) + " <= size <= " + str(string1_length) + " but got " + str(string2_length), ValidationFunction.FAIL)

 else:
 self.store_result("", ValidationFunction.PASS)

Try to solve the Isomorphic Strings problem.


Isomorphic Strings

Try to solve the Isomorphic Strings problem.

Hash Maps

Knowing What to Track

Conclusion

Isomorphic Strings

Statement

Examples

Understand the problem

Figure it out!

Try it yourself