Learn and practice the Top K Elements and Two Heaps patterns to solve coding interview problems.

Speedrun the Oracle Coding Interview: Top Problems in Python

This module will teach you the underlying concepts and equip you with the techniques needed to use heaps to efficiently solve a diverse range of problems. In many problems, we need to find the k most/least frequent or k largest/smallest elements in a given set of elements. Such problems, common in data analysis, natural language processing, online algorithms, as well as in recommendation systems, may be solved using the Top K Elements pattern. The fast insertion and deletion operations possible with heaps make them ideal to implement efficient algorithms for such problems. Further, we can use two heaps when we need to simultaneously keep track of the k largest elements in a set, as well as the k smallest elements in the same set. Extending this idea, each heap may be based on a separate dataset. These techniques are used to solve problems categorized under the Two Heaps pattern.

Heaps

# Statement
Given a string, `str`, rearrange it so that any two adjacent characters are not the same. If such a reorganization of the characters is possible, output any possible valid arrangement. Otherwise, return an empty string.

**Constraints:**
* $1\leq$ `str.length` $\leq500$
* Input string consists of 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 you check that if you’re solving the correct problem:


What is the output if the following string is given as input?

 "programming" 

(Select all that apply.)


What is the output if the following string is given as input?
“programming”
(Select all that apply.)

What is the output if the following string is given as input?

"bbbbaa"

(Select all that apply.)

What is the output if the following string is given as input?
“bbbbaa”
(Select all that apply.)

What is the output if the following string is given as input?

“hello”

(Select all that apply.)

What is the output if the following string is given as input?
“hello”
(Select all that apply.)

Reorganize String 

Reorganize String

# 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.


Implement your solution in the following coding playground:





Help me debug only the function Reorganize String . . I don't need the corrected code.I don't want explanations or code review. Just provide me the exact and to-the-point error that helps me run the code successfully on the test cases provided.

Please help me understand why this code failed for the last failed test case. Don't give me the corrected code. . If yes, then Just provide me the exact and to-the-point error that helps me run the code successfully on the test cases provided.

Your current task is to review only the reorganize_string function and the other function(s) invoked in it/them. Do not review extra/helper files or functions not invoked in the solution function reorganize_string. 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 Top K Elements pattern used? Take your time and review the code.

Please provide a brief time complexity analysis of the function reorganize_string. 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 reorganize_string. 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
        """
        from collections import Counter
        import heapq

        def verify_reorganization(s):
            new_s = ""
            prev = ""
            for c in s:
                if len(new_s) == 0:
                    new_s += c
                    prev = c
                if c == prev:
                    continue
                else:
                    new_s += c
                    prev = c
            return new_s

        def reorganize_string_test(input_string):
            # convert input_string to char_counter
            # store counts of each char along with their occurence
            char_counter = Counter(input_string)

            # initializing heap
            most_freq_chars = []

            # store char and its negative frequency in the array
            for char, count in char_counter.items():
                most_freq_chars.append([-count, char])

            # heapify the array
            heapq.heapify(most_freq_chars)

            # initializing variables
            previous = None
            result = ""

            while len(most_freq_chars) > 0 or previous:

                if previous and len(most_freq_chars) == 0:
                    return ""

                count, char = heapq.heappop(most_freq_chars)
                result = result + char
                count = count + 1

                # pushing the char back to heap
                if previous:
                    heapq.heappush(most_freq_chars, previous)
                    previous = None

                # setting previous to the most recent used char
                if count != 0:
                    previous = [count, char]

            return result + ""

        expected = reorganize_string_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 or (len(expected) !=len(actual)):
            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 expected !=actual and len(expected)==len(actual):
            temp = verify_reorganization(actual);
            if actual == temp:
                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

# importing libraries
from collections import Counter
import heapq

def reorganize_string(str):

    # Replace this placeholder return statement with your code
    
    return ""

reorganize_string (1).yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : abb
    output: 
    - 1 : bab
  - name: "testcase 2"
    inputs:
    - 1: aaaaabbbbbbb
    output:
    - 1 : ""
  - name: "testcase 3"
    inputs:
    - 1: jjjjj
    output:
    - 1: ""
  - name: "testcase 4"
    inputs:
    - 1: aaabc
    output:
    - 1: abaca
  - name: "testcase 5"
    inputs:
    - 1: fofjjb
    output:
    - 1: fofjbj

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
 """
 
 str = self.__inputs[0]

 if not 1 <= len(str) <= 500:
 self.store_result("'str' length should be in the range [1,500]", ValidationFunction.FAIL)
 elif not str.islower() or not str.isalpha():
 self.store_result ("'str' should consist of lowercase English alphabets", ValidationFunction.FAIL)
 else:
 self.store_result("", ValidationFunction.PASS)

Try to solve the Reorganize String problem.


Reorganize String

Try to solve the Reorganize String problem.

Top K Elements

Two Heaps

Conclusion

Reorganize String

Statement

Examples

Understand the problem

Figure it out!

Try it yourself