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

Speedrun the Meta Coding Interview: Top Problems in Python

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

# Statement

For a given string, `st`, find whether or not a permutation of this string is a #key# palindrome: Palindrome is a string of characters that reads the same forwards and backwards. For example, "ababa" and "xyxxyx" are palindromes. #key#. You should return TRUE if such a permutation is possible and FALSE if it isn't possible.

**Constraints:**

* $1 \leq$ `st.length` $\leq 1000$
* The string will contain lowercase English letters.

# Examples





# 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:


The string "abb" has a permutation that's a palindrome.

The string “abb” has a permutation that’s a palindrome.

The string "axbk" has a permutation that's a palindrome.

The string “axbk” has a permutation that’s a palindrome.

Palindrome Permutation

Palindrome Permutation

# 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 `main.py` in the following coding playground. The supporting code template provided in `populating_hashmap.py` is meant to assist in developing your solution to the problem.

# Template for populating the hash map
class hash_map:
    def __init__(self):
        self.hash_map_dict = {}
        
    def insert(self, x):
        if x in self.hash_map_dict.keys():
            self.hash_map_dict[x] += 1
        else:
            self.hash_map_dict[x] = 1

Help me debug only the function(s) `permute_palindrome`. I don't need the corrected code, just some hints on how to use the "Knowing What to Track" pattern to solve this problem. I don't want explanations. Just provide me with the exact error that helps me run the code successfully on the test cases provided.

Please help me understand why this code failed for the provided failed test case. Don't give me the corrected code. Just some hints on how to use the "Knowing What to Track" pattern to improve my solution or fix the error. First, check whether the given pattern is used or not. If yes, then Just provide me the exact error that helps me run the code successfully on the test cases provided.

Your current task is to review only the `permute_palindrome` function(s) and the other function(s) invoked in it/them. Do not review extra/helper files or functions not invoked in the solution function `permute_palindrome`. Do not review the code of data structures 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. Also, answer the following questions: Is the "Knowing What to Track" pattern used? Take your time and review the code.

Please provide a brief time complexity analysis of the function(s) `permute_palindrome`. While calculating time complexity, include the time complexity of built-in Python functions invoked by the code. The answer should be to the point and in a few lines.

Please provide a brief space complexity analysis of the function(s) `permute_palindrome`. While calculating space complexity, include the space complexity of built-in Python functions invoked by the code. 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). The answer should be to the point and in a few lines.

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 permute_palindrome_eval(st):
 frequencies = {}
 index = 0
 for i in st:
 index += 1
 if i in frequencies:
 frequencies[i] += 1
 else:
 frequencies[i] = 1
 count = 0
 for ch in frequencies.keys():
 if frequencies[ch] % 2:
 count += 1

 if count <= 1:
 return True
 else:
 return False
 
 expected = permute_palindrome_eval(self.__inputs[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 

 if json.dumps(expected) == json.dumps(self.__actual_outputs[0]):
 expected_outputs.append(expected)
 self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
 else:
 expected_outputs.append(expected)
 self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)

 return self.__edu_result

from populating_hashmap import *


def permute_palindrome(st):

    # Replace this placeholder return statement with your code
    return False


PrivateTestCases.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : "abab"
    output: 
    - 1 : True

  - name: "testcase 2"
    inputs:
    - 1 : "peas"
    output: 
    - 1 : False

  - name: "testcase 3"
    inputs:
    - 1 : "racecar"
    output: 
    - 1 : True

  - name: "testcase 4"
    inputs:
    - 1 : "code"
    output: 
    - 1 : False

  - name: "testcase 5"
    inputs:
    - 1 : "baefeab"
    output: 
    - 1 : True



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

def validate_inputs(self) -> None:
 """
 Validate the string s based on the given constraints.
 Store the result using self.store_result(error_msg, status).
 return: void
 """
 s = self.__inputs[0]

 if not (1 <= len(s) <= 1000):
 self.store_result("String length should be in the range 1 ≤ st.length ≤ 1000", ValidationFunction.FAIL)
 return
 elif not s.islower():
 self.store_result("String 'st' should consist of lowercase English letters only", ValidationFunction.FAIL)
 return
 else:
 self.store_result("", ValidationFunction.PASS)

Try to solve the Palindrome Permutation problem.

Hash Maps

Knowing What to Track

Conclusion

Palindrome Permutation

Statement

Examples

Understand the problem

Figure it out!

Try it yourself