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

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

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 the given stream of message requests and their timestamps as input, you must implement a logger rate limiter system that decides whether the current message request is displayed. The decision depends on whether the same message has already been displayed in the last $S$ seconds. If yes, then the decision is FALSE, as this message is considered a duplicate. Otherwise, the decision is TRUE.

> **Note:** Several message requests, though received at different timestamps, may carry identical messages.

**Constraint:**

* $1 \leq$ `request.length` $\leq 10^{2}$
* $0 \leq$ `timestamp` $\leq 10^{3}$
* Timestamps are in ascending order.
* Messages can be written in lowercase or uppercase English alphabets.

# Examples

> **Note:** In the following examples, the time limit, $S$, is set to $7$.

# 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:

TRUE
 
FALSE
 
FALSE
 
TRUE
 
FALSE
 
FALSE

TRUE
 
TRUE
 
FALSE
 
TRUE
 
TRUE
 
FALSE

Suppose the time limit for the following timestamps is 5. What will be the correct output sequence?

<center> <img src="https://www.educative.io/api/collection/10370001/5500262945128448/page/6644512940359680/image/5425483472961536?page_type=collection_lesson" width="350" height="200">

Suppose the time limit for the following timestamps is 5. What will be the correct output sequence?
<center> <img src="https://www.educative.io/api/collection/10370001/5500262945128448/page/6644512940359680/image/5425483472961536?page_type=collection_lesson" width="350" height="200">

TRUE
 
TRUE
 
TRUE
 
FALSE
 
TRUE
 
TRUE

TRUE
 
TRUE
 
FALSE
 
FALSE
 
TRUE
 
FALSE

TRUE
 
TRUE
 
TRUE
 
FALSE
 
TRUE
 
FALSE

Suppose the time limit for the following timestamps is 5. What will be the correct output sequence?

<center> <img src="https://www.educative.io/api/collection/10370001/5500262945128448/page/6644512940359680/image/5374349739819008?page_type=collection_lesson" width="350" height="200">

Suppose the time limit for the following timestamps is 5. What will be the correct output sequence?
<center> <img src="https://www.educative.io/api/collection/10370001/5500262945128448/page/6644512940359680/image/5374349739819008?page_type=collection_lesson" width="350" height="200">

Logger Rate Limiter

Logger Rate Limiter

# 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:

> **Note:** In the following test cases, the time limit, $S$, is set to $7$.

#include <iostream>
#include <unordered_map>
#include <vector>

class RequestLogger {
 private:
 std::unordered_map<std::string, int> requests;
 int timeLimit;

 public:

 RequestLogger(int newTimeLimit){
 // Initialize your data structure here
 }
 
 bool MessageRequestDecision(int timestamp, std::string request) {
 // Replace the placeholder return statement with your code
 return false;
 }
};

Help me debug only the function Logger Rate Limiter . . 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 MessageRequestDecision function and the other function(s) invoked in it/them. Do not review extra/helper files or functions not invoked in the solution function MessageRequestDecision. 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 Hash Maps pattern used? Take your time and review the code.

Please provide a brief time complexity analysis of the function MessageRequestDecision. While calculating time complexity, include the time complexity of built-in C++ 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 MessageRequestDecision. While calculating space complexity, include the space complexity of built-in C++ 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

TwoDArray

#include <string>

using namespace std;

class TwoDArray : public DataStructure
{

 // define class attributes

private:
 void generateError(string data)
 {
 cerr << "TwoDArray is not parsable: " << data;
 exit(-1);
 }

public:
 std::vector<vector<string>> val;
 std::vector<bool> val2;

 TwoDArray()
 {
 // constructor
 }
 TwoDArray(std::vector<bool> v)
 {
 this->val2 = v;
 // constructor
 }
 
 // return value will be passed to user program
 // void *construct(string new_value, int typeOfDs)
 // {
 // json j_complete = json::parse(new_value);
 // std::vector<std::vector<string>> temp = j_complete;
 // this->val = temp;
 // // cout << this->val.size();
 // return this;
 // // parse test case in json string 'value' to your desired data structure
 // }
 void *construct(string new_value, int typeOfDs)
{
 json j_complete = json::parse(new_value);

 // Ensure that the top-level structure is an array
 if (!j_complete.is_array()) {
 generateError("Invalid input format. Expected an array.");
 }

 std::vector<std::vector<string>> temp;

 // Iterate through the array and TwoDArray each element to a vector of strings
 for (const auto& element : j_complete) {
 // Ensure that each element is an array of size 2
 if (!element.is_array() || element.size() != 2) {
 generateError("Invalid element format. Expected an array of size 2.");
 }

 // Extract int and string from the array
 int intValue = element[0];
 string stringValue = element[1];

 // TwoDArray int to string and add both to the inner vector
 temp.push_back({to_string(intValue), stringValue});
 }

 this->val = temp;

 return this;
}


 // input param contains return value of user program
 string traverse(void *input, int typeOfDs)
 {
 TwoDArray * custom_ds = (TwoDArray *)input; 
 json result = (json)(custom_ds->val2);
 return result.dump();
 // TwoDArray your data structure 'input' to a json string representing a test case output
 }

 // override operator<< for your data structure if required
};

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
        """
        class RequestLogger:

            # initailization of requests hash map
            def __init__(self, time_limit):
                self.requests = {}
                self.limit = time_limit

            # function to accept and deny message requests
            def message_request_decision(self, timestamp, request):

                if request not in self.requests or timestamp - self.requests[request] >= self.limit:
                    self.requests[request] = timestamp
                    return True

                else:
                    return False

        # -----------------------------------------------------------------------------------
        # -----------------------------------------------------------------------------------
        # multiple outputs will be added at each index respectively for a single test_case
        expected_outputs = [] 

        def main_eval(input_1):
            new_requests = RequestLogger(7)
            result = []

            # loop to execute over the input message requests
            for i in range(len(input_1)):
                # print(input_1, ": ", input_2)
                res = new_requests.message_request_decision(input_1[i][0], input_1[i][1])
                result.append(res)
            
            return result
            
        expected = main_eval(self.__inputs[0])
        # store the 1st expected output that should be displayed to the user 
        actual = self.__actual_outputs[0]

        if expected == actual:
            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



#include <vector>
#include <queue>
#include "RequestLogger.cpp"
#include <bits/stdc++.h>
#include "TwoDArray.cpp"
#include <string>
using namespace std;

TwoDArray RequestLoggerMain(TwoDArray input_1){
 RequestLogger new_requests = RequestLogger(7);
 
 TwoDArray result = *(new TwoDArray());
 
 // loop to execute over the input message requests
 for (int i = 0; i < input_1.val.size(); i++){
 int one = stoi(input_1.val[i][0]);
 bool res = new_requests.MessageRequestDecision(one, input_1.val[i][1]);
 result.val2.push_back(res);
 }
 return result;
 
}

PrivateTestCases.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : [[1, "good morning"], [5, "good morning"], [9, "i need coffee"], [10, "hello world"], [11, "good morning"], [15, "i need coffee"], [17, "hello world"], [25, "i need coffee"]]
    output:
    - 1 : [True, False, True, True, True, False, True, True]

  - name: "testcase 2"
    inputs:
    - 1 : [[1, "good morning"], [5, "hello world"], [6, "good morning"], [7, "good morning"], [15, "hello world"]]
    output:
    - 1 : [True, True, False, False, True]

  - name: "testcase 3"
    inputs:
    - 1 : [[3, "pass"], [5, "fail"], [6, "pass"], [14, "pass"], [17, "pass"], [26, "fail"], [27, "fail"]]
    output:
    - 1 : [True, True, False, True, False, True, False]

  - name: "testcase 4"
    inputs:
    - 1 : [[1, "sunny"], [5, "sunny"], [6, "not sunny"], [7, "raining"], [15, "snowing"], [16, "sunny"], [17, "not sunny"], [18, "raining"], [19, "snowing"]]
    output:
    - 1 : [True, False, True, True, True, True, True, True, False]

  - name: "testcase 5"
    inputs:
    - 1 : [[1, "good morning"], [5, "good morning"], [9, "i need coffee"], [10, "hello world"], [11, "good moring"], [15, "i need coffee"], [17, "hello world"], [25, "i need coffee"]]
    output:
    - 1 : [True, False, True, True, True, False, True, True]

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
 """
 min_length = 1
 max_length = 10 ** 3

 requests = self.__inputs[0]
 def is_valid_2d_array(arr):
 if not isinstance(arr, list) or not all(isinstance(row, list) for row in arr):
 return False # Not a valid 2D array if it's empty or contains non-list elements

 for row in arr:
 if any(elem is None or isinstance(elem, bool) for elem in row):
 return False # Not a valid 2D array if any element in a row is None

 for elem in row:
 if isinstance(elem, tuple):
 # Check if the tuple contains an int and a str
 if not (len(elem) == 2 and isinstance(elem[0], int) and isinstance(elem[1], str)):
 return False
 elif not (isinstance(elem, int) or isinstance(elem, str)):
 return False # Not a valid 2D array if any element in a row is not an integer or a tuple with int and str

 return True # Valid 2D array
 def has_non_ascii(text):
 return any(ord(char) > 127 for char in text)


 # Inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 1
 if not is_valid_2d_array(requests):
 self.store_result ("Not a valid test case", ValidationFunction.FAIL)
 elif not (min_length <= len(requests) <= max_length):
 self.store_result("The length of 'request' should be between 1 and 1000", ValidationFunction.FAIL)
 elif any(len(request) != 2 for request in requests):
 self.store_result("The length of message should be 2", ValidationFunction.FAIL)
 elif any( not (isinstance(request[0], int)) or request[0]is False or request[0] is True for request in requests):
 self.store_result("'timestamp' of each message should be an integer", ValidationFunction.FAIL)
 elif any(not 0<=request[0]<=1000 for request in requests):
 self.store_result("'timestamp' should be between 0 and 10^3", ValidationFunction.FAIL)
 elif any( not (1 <= len(str(request[1])) <= 1000) for request in requests):
 self.store_result("The length of the 'requests' should be between 1 and 1000",ValidationFunction.FAIL)
 elif any( not isinstance(request[1], str) for request in requests):
 self.store_result("'request' should be a string", ValidationFunction.FAIL)
 elif any(any(char.isnumeric() or not char.isalpha() and not char.isspace() for char in str(request[1])) for request in requests):
 self.store_result("'request' should be a lowercase or uppercase letters", ValidationFunction.FAIL)
 elif any(has_non_ascii(str(request[1])) for request in requests):
 self.store_result("'request' should be a lowercase or uppercase letters.", ValidationFunction.FAIL)
 elif any(requests[i] > requests[i + 1] for i in range(len(requests) - 1)):
 self.store_result("'timestamp' should be in ascending order", ValidationFunction.FAIL)
 else:
 self.store_result("", ValidationFunction.PASS)

Try to solve the Logger Rate Limiter problem.

Hash Maps

Knowing What to Track

Conclusion

Logger Rate Limiter

Statement

Examples

Understand the problem

Figure it out!

Try it yourself