Learn and practice the Sliding Window, and Union Find patterns to solve coding interview problems.

Speedrun the Meta Coding Interview: Top Problems in C++

Each pattern 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 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

Given two strings, `s` and `t`, find the minimum window substring in `s`, which has the following properties:

1. It is the shortest substring of `s` that includes all of the characters present in `t`.

2.  It must contain at least the same frequency of each character as in `t`.

3. The order of the characters does not matter here.

> **Note:** If there are multiple valid minimum window substrings, return any one of them.

**Constraints:**

* Strings `s` and `t` consist of uppercase and lowercase English characters.

* 1 $\leq$ `s.length`, `t.length` $\leq 10^3$

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

`s` = “bbaac”

`t` = “aba”



What is the output if the following strings are given as input?
<code>s</code> = “bbaac”
<code>t</code> = “aba”

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

`s` = “AbabbbAbaA”

`t` = “Bab”


What is the output if the following strings are given as input?
<code>s</code> = “AbabbbAbaA”
<code>t</code> = “Bab”

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

`s` = “cabwefgewcwaefgcf”

`t` = “cae”

What is the output if the following strings are given as input?
<code>s</code> = “cabwefgewcwaefgcf”
<code>t</code> = “cae”

Minimum Window Substring

Minimum Window Substring

# 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: `MinWindow`\n- Candidate's submitted solution code: USER_CODE\n- Error: ERROR_DESCRIPTION\n- Failed test case: FAILED_TEST_CASE\n- Coding language: `C++`\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 `MinWindow` 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 `MinWindow`.\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) `MinWindow`. \n- While calculating time complexity, include the time complexity of built-in C++ 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) `MinWindow`. \n- While calculating space complexity, include the space complexity of built-in C++ 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 min_window(s, t):
 if t == "":
 return ""

 req_count = {}
 window = {}
 result = []

 for c in t:
 req_count[c] = 1 + req_count.get(c, 0)

 for c in t:
 window[c] = 0

 current, required = 0, len(req_count)

 res, res_len = [-1, -1], float("infinity")

 left = 0
 for right in range(len(s)):
 c = s[right]

 if c in t:
 window[c] = 1 + window.get(c, 0)

 if c in req_count and window[c] == req_count[c]:
 current += 1

 while current == required:
 result.append(s[left:right+1])
 if (right - left + 1) < res_len:
 res = [left, right]
 res_len = (right - left + 1)
 
 if s[left] in t:
 window[s[left]] -= 1

 if s[left] in req_count and window[s[left]] < req_count[s[left]]:
 current -= 1
 left += 1
 left, right = res

 min_len = len(s[left:right+1])

 filtered_strings = [s for s in result if len(s) <= min_len]
 return filtered_strings


 # multiple outputs will be added at each index respectively for a single test_case
 expected_outputs = []

 expected = ""
 if min_window(self.__inputs[0], self.__inputs[1]):
 expected = min_window(self.__inputs[0], self.__inputs[1])[0]
 
 # store the 1st expected output that should be displayed to the user 
 expected_outputs.append(expected)

 if self.__actual_outputs[0] == "" and not min_window(self.__inputs[0], self.__inputs[1]):
 
 self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
 else:
 if sorted(expected) == sorted(self.__actual_outputs[0]):
 # expected_outputs.append(expected)
 self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
 else:
 self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)

 return self.__edu_result

string MinWindow(string s, string t) {

    // Replace this placeholder return statement with your code
    return "";
}

minimum_window_substring.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : "ABCD"
    - 2 : "ABC"
    output: 
    - 1 : "ABC"
  - name: "testcase 2"
    inputs:
    - 1: "XYZYX"
    - 2: "XYZ"
    output:
    - 1 : "XYZ"
  - name: "testcase 3"
    inputs:
    - 1: "ABXYZJKLSNFC"
    - 2: "ABC"
    output:
    - 1 : "ABXYZJKLSNFC"
  - name: "testcase 4"
    inputs:
    - 1: "AAAAAAAAAAA"
    - 2: "A"
    output:
    - 1 : "A"
  - name: "testcase 5"
    inputs:
    - 1: "ABDFGDCKAB"
    - 2: "ABCD"
    output:
    - 1 : "DCKAB"

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

 s = self.__inputs[0]
 s_lower_bound = 1
 s_upper_bound = 10**3

 t = self.__inputs[1]
 t_lower_bound = 1
 t_upper_bound = 10**3

 valid_characters = [char for char in (string.ascii_lowercase + string.ascii_uppercase)]

 def contains_valid_characters(s, chars):
 for char in s:
 if char not in chars:
 return False
 return True

 def list_to_string(char_list):
 return "[" + ', '.join(map(repr, char_list)) + "]"

 # inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 1
 if len(s) < s_lower_bound or len(s) > s_upper_bound:
 self.store_result ("expected 's' to have" + str(s_lower_bound) + " <= size <= " + str(s_upper_bound) + " but got " + str(len(s)), ValidationFunction.FAIL)

 elif len(t) < t_lower_bound or len(t) > t_upper_bound:
 self.store_result ("expected 't' to have" + str(t_lower_bound) + " <= size <= " + str(t_upper_bound) + " but got " + str(len(t)), ValidationFunction.FAIL)

 elif not contains_valid_characters(s, valid_characters):
 self.store_result ("'s' must consist of uppercase or lowercase characters only", ValidationFunction.FAIL)

 elif not contains_valid_characters(t, valid_characters):
 self.store_result ("'t' must consist of uppercase or lowercase characters only", ValidationFunction.FAIL)

 else:
 self.store_result("", ValidationFunction.PASS)

Try to solve the Minimum Window Substring problem.

Sliding Window

Union Find

Conclusion

Minimum Window Substring

Statement

Examples

Understand the problem

Figure it out!

Try it yourself