Learn and practice the Backtracking, Subsets, and Dynamic Programming patterns to solve coding interview problems.

Grokking Grind 75 in Python: Mastery through Coding Patterns

Building a strong foundation for systematically tackling complex coding interview challenges is crucial. This module explores key patterns for addressing complex coding interview challenges. It covers the Backtracking and Subsets patterns for systematic problem-solving, each suited to different types of problems. Backtracking excels in decision tree exploration, while Subsets is ideal for generating power sets. The module also delves into Dynamic Programming, which optimizes complex problems by breaking them into smaller subproblems. Techniques like memoization and tabulation enhance efficiency. Overall, the module teaches us how to dissect challenging problems systematically and arrive at optimal solutions.

Effective Decision-making

# Statement

Given an input string, `word`, return all possible permutations of the string.

> **Note:** The order of permutations does not matter. 

**Constraints:**

* All characters in `word` are unique.

* $1 \leq$ `word.length` $\leq 6$
* All characters in `word` are lowercase English letters.

# 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:

["xyz", "xzy", "yxz", "yzx", "zyx", "zxy"]

["xyz", "xzy", "xxz", "yzx", "zyx", "zxz"]

["xyz", "xzy", "xxz", "yzx", "zyx", "zxy"]

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

Input string = "xyz"

What should be the output if the following string is given as input?
Input string = “xyz”

["ogc", "ocg", "cog", "cgo", "goc", "gco"]

["gog", "gco", "ogc", "ocg", "cog", "cgo"]

["goc", "gco", "ogc", "ocg", "cog", "cgo"]

What should be the output if the following string is given as input? (Select all possible options)

Input string = "goc"

What should be the output if the following string is given as input? (Select all possible options)
Input string = “goc”

How many permutations are possible for an input string of length 4?

How many permutations are possible for an input string of length 4?

Permutations

Permutations

# 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:

# 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: `permute_word`\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 `permute_word` 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 `permute_word`.\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) `permute_word`. \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) `permute_word`. \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 swap_char(word, i, j):
            swap_index = list(word)
            swap_index[i], swap_index[j] = swap_index[j], swap_index[i]

            return ''.join(swap_index)


        def permute_string_rec(word, current_index, result):
            # Prevents adding duplicate permutations
            if current_index == len(word) - 1:
                result.append(word)

                return

            for i in range(current_index, len(word)):
                # swaps character for each permutation
                swapped_str = swap_char(word, current_index, i)

                # recursively calls itslef to find each permuation
                permute_string_rec(swapped_str, current_index + 1, result)


        def permute_word(word):
            result = []

            # Starts finding permuations from start of string
            permute_string_rec(word, 0, result)

            return result

        def compareResult(expected, actual_output):
            expected.sort()
            actual_output.sort()
            
            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
        expected = permute_word(self.__inputs[0])
        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

def permute_word(word):
    result = []

    # Replace this placeholder return statement with your code
    return result


PrivateTestCases.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : "abcd"
    output: 
    - 1 : ["abcd", "abdc", "acbd", "acdb", "adcb", "adbc", "bacd", "badc", "bcad", "bcda", "bdca", "bdac", "cbad", "cbda", "cabd", "cadb", "cdab", "cdba", "dbca", "dbac", "dcba", "dcab", "dacb", "dabc"]

  - name: "testcase 2"
    inputs:
    - 1: "bad"
    output:
    - 1 : ["bad", "bda", "abd", "adb", "dab", "dba"]

  - name: "testcase 3"
    inputs:
    - 1: "ab"
    output:
    - 1: ["ab", "ba"]

  - name: "testcase 4"
    inputs:
    - 1: "xyz"
    output:
    - 1: ["xzy", "xyz", "zxy", "zyx", "yzx", "yxz"]

  - name: "testcase 5"
    inputs:
    - 1: "a"
    output:
    - 1: ["a"]

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 the function
 store the result using the self.store_result(error_msg, status)
 return : void
 """ 
 word=self.__inputs[0]
 min_length= 1
 max_length= 6

 if any(num is None for num in word):
 self.store_result ("Not a valid test case", ValidationFunction.FAIL) 
 elif len(word) < min_length or len(word) > max_length:
 self.store_result("Input length should be between 1 and 6", ValidationFunction.FAIL)
 elif any(not wordd.islower() for wordd in word):
 self.store_result("Each word should be a lowercase English letter", ValidationFunction.FAIL) 
 
 elif len(word) != len(set(word)):
 self.store_result("Input should contain only unique characters", ValidationFunction.FAIL)
 else:
 self.store_result("", ValidationFunction.PASS)

Backtracking

Subsets

Dynamic Programming

Conclusion

Permutations

Statement

Understand the problem

Figure it out!

Try it yourself