Learn and practice the Graphs, Tries, and Custom Data Structures patterns to solve coding interview problems.

Speedrun the Netflix Coding Interview: Top Problems in Java

Proficiency in advanced data structures is a marker of a highly experienced engineer, and interviewers use such questions to finetune how they grade candidates. This module teaches you the use of two advanced data structures—graphs and tries—to solve relatively complex problems. To solve problems with very specific requirements that may not be handled by standard data structures, we gain experience in the advanced skill of the design, implementation, and efficient use of custom data structures.

Advanced Data Structures

["JFK", "ABX", "JFK", "ABC", "COA", "JFK"]

Given the following list of `tickets`, what is the correct itinerary starting from `“JFK”`?

`tickets` $=$ [[“JFK”, “ABC”], [“ABC”, “COA”], [“JFK”, “ABX”], [“COA", "JFK”]]

Given the following list of <code>tickets</code>, what is the correct itinerary starting from <code>“JFK”</code>?
<code>tickets</code> <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo>=</mo></mrow><annotation encoding="application/x-tex">=</annotation></semantics></math>= [[“JFK”, “ABC”], [“ABC”, “COA”], [“JFK”, “ABX”], [“COA&quot;, &quot;JFK”]]

["WXY", "ABC", "XYZ", "JFK", "XYZ", "ABC", "JFK"]

["JFK", "ABC", "XYZ", "JFK", 
"ABC", "XYZ", "WXY"]

["JFK", "ABC", "XYZ", "JFK", "XYZ", "ABC", "WXY"]

["JFK", "XYZ", "ABC", "XYZ", "JFK", "ABC", "WXY"]

Given the following list of `tickets`, what is the correct itinerary starting from `“JFK”`?

`tickets` $=$ [[“JFK”, “ABC”], [“JFK”, “XYZ”], [“ABC”, “XYZ”], [“XYZ”, “JFK”], [“ABC”, “WXY”], [“XYZ”, “ABC”]]

Given the following list of <code>tickets</code>, what is the correct itinerary starting from <code>“JFK”</code>?
<code>tickets</code> <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo>=</mo></mrow><annotation encoding="application/x-tex">=</annotation></semantics></math>= [[“JFK”, “ABC”], [“JFK”, “XYZ”], [“ABC”, “XYZ”], [“XYZ”, “JFK”], [“ABC”, “WXY”], [“XYZ”, “ABC”]]

["JFK", "CCC", "DDD", "JFK", "AAA", "BBB", "JFK"]

["JFK", "AAA", "BBB", "JFK", "CCC", "DDD", "JFK"]

["JFK", "DDD", "CCC", "JFK", "BBB", "AAA", "JFK"]

["JFK", "AAA", "BBB", "JFK", "CCC", "DDD"]

Given the following list of `tickets`, what is the correct itinerary starting from `“JFK”`?

`tickets` $=$ [[“JFK”, “AAA”], [“AAA”, “BBB”], [“BBB", “JFK”], [“JFK”, “CCC”], [“CCC”, “DDD”], [“DDD", “JFK”]]

Given the following list of <code>tickets</code>, what is the correct itinerary starting from <code>“JFK”</code>?
<code>tickets</code> <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo>=</mo></mrow><annotation encoding="application/x-tex">=</annotation></semantics></math>= [[“JFK”, “AAA”], [“AAA”, “BBB”], [“BBB&quot;, “JFK”], [“JFK”, “CCC”], [“CCC”, “DDD”], [“DDD&quot;, “JFK”]]

Reconstruct Itinerary

Reconstruct Itinerary

std::vector<std::string> findItinerary(std::vector<std::vector<std::string>>& tickets) {

 return {};
}

import java.util.*;

public class Solution {
 public static List<String> findItinerary(List<List<String>> tickets) {
 
 // Replace this placeholder return statement with your code
 return new ArrayList<>();
 }
}

# 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: `findItinerary`\n- Candidate's submitted solution code: USER_CODE\n- Error: ERROR_DESCRIPTION\n- Failed test case: FAILED_TEST_CASE\n- Coding language: `Java`\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 `findItinerary` 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 `findItinerary`.\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) `findItinerary`. \n- While calculating time complexity, include the time complexity of built-in Java 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) `findItinerary`. \n- While calculating space complexity, include the space complexity of built-in Java 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.

TwoDArray

#include <string>

using namespace std;

class TwoDArray : public DataStructure
{

 // define class attributes

private:
 void generateError(string data)
 {
 cerr << "MyTwoDArray is not parsable: " << data;
 exit(-1);
 }

public:
 vector<vector<string>> val;
 TwoDArray()
 {
 // constructor
 }
 
 // return value will be passed to user program
 void *construct(string str, int typeOfDs)
 {
 json j_complete = json::parse(str);
 vector<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
 }

 // input param contains return value of user program
 string traverse(void *input, int typeOfDs)
 {
 return "";
 // convert your data structure 'input' to a json string representing a test case output
 }

 // override operator<< for your data structure if required
};

import java.util.*;
import java.io.IOException; 
import com.fasterxml.jackson.databind.*; 
import com.fasterxml.jackson.core.type.TypeReference;

import ds_v1.DataStructure.DataStructure;

public class TwoDArray extends DataStructure {

 // define class attributes
 public List<List<String>> arr;

 private void generateError(String data) {
 System.err.println("TwoDArray is not parsable: " + data);
 System.exit(-1);
 }

 public TwoDArray() {
 // constructor
 }

 public TwoDArray(List<List<String>> data) {
 // constructor
 this.arr = new ArrayList<List<String>>();
 arr = data;
 }

 public String toString() {
 // override toString() for your data structure
 return this.arr.toString();
 }

 private void construct_nested_string_arr(String new_value) {
 // ArrayList<ArrayList<String>> parsed = null;
 try {
 this.arr = new ObjectMapper().readValue(new_value, new TypeReference<List<List<String>>>() {
 });
 } catch (IOException e) {
 }
 // return parsed;
 }

 // return value will be passed to user program
 @Override
 public TwoDArray construct(String value, Integer type_of_ds) {
 // parse test case in json string 'value' to your desired data structure
 construct_nested_string_arr(value);
 return new TwoDArray(this.arr);
 }

 // input param contains return value of user program
 @Override
 public String traverse(Object input, Integer type_of_ds) {
 // convert your data structure 'input' to a json string representing a test case output
 return input.toString();
 }

}

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 defaultdict

        def find_itinerary_eval(tickets):
            flight_map = defaultdict(list)

            for departure, arrival in tickets:
                flight_map[departure].append(arrival)

            for departure in flight_map:
                flight_map[departure].sort(reverse=True)

            result=[]
            dfs_traversal('JFK', flight_map, result)

            return result[::-1]

        def dfs_traversal(current, flight_map, result):
            destinations = flight_map[current]

            while destinations:
                next_destination = destinations.pop()
                dfs_traversal(next_destination, flight_map, result)
            result.append(current)
        
        expected = find_itinerary_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 
        expected_outputs.append(expected)

        if json.dumps(expected) == json.dumps(self.__actual_outputs[0]):
            self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
        else:
            self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)

        return self.__edu_result

import java.util.*;

public class Main{
 public static ArrayList<String> findItineraryWrapper(TwoDArray ingredients) {

 List<String> temp = Solution.findItinerary(ingredients.arr);
 ArrayList<String> result = new ArrayList<String>(temp);
 // Collections.sort(result);
 return result;
 }
}

reconstruct_itinerary_private_testcases (2).yaml

testcases:
  - name: 'testcase 1 - Single Flight Itinerary'
    inputs:
      - 1: [['JFK', 'IDN']]
    output:
      - 1: ['JFK', 'IDN']
  - name: 'testcase 2 - Multiple Flights Simple Path'
    inputs:
      - 1: [['JFK', 'MLW'], ['MLW', 'XKB'], ['XKB', 'RUE'], ['RUE', 'QNW'], ['QNW', 'DJC'], ['DJC', 'RUK'], ['RUK', 'RCE'], ['RCE', 'YAM'], ['YAM', 'KGF'], ['KGF', 'QRH'], ['QRH', 'PDB'], ['PDB', 'GSR'], ['GSR', 'HZY'], ['HZY', 'REC'], ['REC', 'CKI'], ['CKI', 'UEI'], ['UEI', 'LWM']]
    output:
      - 1: ['JFK', 'MLW', 'XKB', 'RUE', 'QNW', 'DJC', 'RUK', 'RCE', 'YAM', 'KGF', 'QRH', 'PDB', 'GSR', 'HZY', 'REC', 'CKI', 'UEI', 'LWM']
  - name: 'testcase 3 - Unique Itinerary'
    inputs:
      - 1: [['JFK', 'QBO'], ['QBO', 'KLY'], ['KLY', 'XBB'], ['XBB', 'WFV'], ['WFV', 'WXC'], ['WXC', 'HKJ'], ['HKJ', 'YLK'], ['YLK', 'LIG'], ['LIG', 'GHX'], ['GHX', 'VJQ'], ['VJQ', 'XBR'], ['XBR', 'PJU'], ['PJU', 'ITU'], ['ITU', 'XTP'], ['XTP', 'POX'], ['POX', 'NZI'], ['NZI', 'PVZ'], ['PVZ', 'WGI'], ['WGI', 'GNJ'], ['GNJ', 'LIE'], ['LIE', 'GPA'], ['GPA', 'RJE'], ['RJE', 'LBQ'], ['LBQ', 'ELU'], ['ELU', 'PEI'], ['PEI', 'QVO'], ['QVO', 'ADZ'], ['ADZ', 'STH'], ['STH', 'DCT'], ['DCT', 'OSB'], ['OSB', 'BIG'], ['BIG', 'KOH'], ['KOH', 'QDJ']]
    output:
      - 1: ['JFK', 'QBO', 'KLY', 'XBB', 'WFV', 'WXC', 'HKJ', 'YLK', 'LIG', 'GHX', 'VJQ', 'XBR', 'PJU', 'ITU', 'XTP', 'POX', 'NZI', 'PVZ', 'WGI', 'GNJ', 'LIE', 'GPA', 'RJE', 'LBQ', 'ELU', 'PEI', 'QVO', 'ADZ', 'STH', 'DCT', 'OSB', 'BIG', 'KOH', 'QDJ']
  - name: 'testcase 4 - Bidirectional Paths'
    inputs:
      - 1: [['JFK', 'OBU'], ['OBU', 'JFK'], ['JFK', 'KNJ'], ['KNJ', 'JFK'], ['JFK', 'FBF'], ['FBF', 'JFK'], ['JFK', 'SXL'], ['SXL', 'JFK'], ['JFK', 'UND'], ['UND', 'JFK'], ['JFK', 'HKO'], ['HKO', 'JFK'], ['JFK', 'IUB'], ['IUB', 'JFK'], ['JFK', 'LOG'], ['LOG', 'JFK'], ['JFK', 'NRN'], ['NRN', 'JFK'], ['JFK', 'YUU'], ['YUU', 'JFK'], ['JFK', 'VKL'], ['VKL', 'JFK'], ['JFK', 'LWE'], ['LWE', 'JFK']]
    output:
      - 1: ['JFK', 'FBF', 'JFK', 'HKO', 'JFK', 'IUB', 'JFK', 'KNJ', 'JFK', 'LOG', 'JFK', 'LWE', 'JFK', 'NRN', 'JFK', 'OBU', 'JFK', 'SXL', 'JFK', 'UND', 'JFK', 'VKL', 'JFK', 'YUU', 'JFK']
  - name: 'testcase 5 - Multiple Branches And Cycles'
    inputs:
      - 1: [["JFK","SFO"],["JFK","ATL"],["SFO","ATL"],["ATL","JFK"],["ATL","SFO"]]
   

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

 """
 from collections import defaultdict

 def find_itinerary(tickets):
 flight_map = defaultdict(list)
 result = []

 for departure, arrival in tickets:
 flight_map[departure].append(arrival)

 for departure in flight_map:
 flight_map[departure].sort(reverse=True)

 dfs_traversal('JFK', flight_map, result)

 return result[::-1]

 def dfs_traversal(current, flight_map, result):
 destinations = flight_map[current]

 while destinations:
 next_destination = destinations.pop()
 dfs_traversal(next_destination, flight_map, result)
 result.append(current)

 def has_unique_itinerary(tickets):
 flight_map = defaultdict(list)

 for departure, arrival in tickets:
 flight_map[departure].append(arrival)

 for departure in flight_map:
 flight_map[departure].sort(reverse=True)

 visit_stack = ['JFK']
 visit_count = defaultdict(int)
 unique_path = []

 while visit_stack:
 current = visit_stack[-1]
 if flight_map[current]:
 next_destination = flight_map[current].pop()
 visit_stack.append(next_destination)
 visit_count[(current, next_destination)] += 1
 else:
 unique_path.append(visit_stack.pop())

 # Check if all edges (tickets) are used exactly once in the unique path
 return len(unique_path) == len(tickets) + 1
 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
 if not all(isinstance(elem, str) and len(elem) == 3 for elem in row):
 return False
 return True

 tickets = self.__inputs[0]
 if isinstance(tickets, bool):
 self.store_result("Input should be a valid 2D String array", ValidationFunction.FAIL)
 return
 elif not is_valid_2d_array(tickets):
 self.store_result("Not a valid 2D String array", ValidationFunction.FAIL)
 return
 elif not has_unique_itinerary(tickets):
 self.store_result("The itinerary must have a unique valid solution.", ValidationFunction.FAIL)
 return

 # Check if the input is an empty array or contains an empty list
 elif not tickets or (len(tickets) == 1 and tickets[0] == []):
 self.store_result("Invalid input!", ValidationFunction.FAIL)
 return
 
 # Check the number of tickets
 elif not (1 <= len(tickets) <= 300):
 self.store_result("The number of tickets must be between 1 and 300.", ValidationFunction.FAIL)
 return
 
 # Iterate through each ticket to validate its constraints
 for ticket in tickets:
 if len(ticket) != 2:
 self.store_result("Each ticket must contain exactly 2 elements.", ValidationFunction.FAIL)
 return
 fromi, toi = ticket

 # Check the length of each airport code
 if len(fromi) != 3 or len(toi) != 3:
 self.store_result("Each airport code must be exactly 3 characters long.", ValidationFunction.FAIL)
 return
 
 # Check that airport codes consist of uppercase English letters
 if not (fromi.isalpha() and fromi.isupper()) or not (toi.isalpha() and toi.isupper()):
 self.store_result("Airport codes must consist of uppercase English letters.", ValidationFunction.FAIL)
 return

 # Check that the fromi and toi are not the same
 if fromi == toi:
 self.store_result("The departure and arrival airports must be different.", ValidationFunction.FAIL)
 return
 

 # If all checks pass
 self.store_result("", ValidationFunction.PASS)

Try to solve the Reconstruct Itinerary problem.

Graphs

Trie

Custom Data Structures

Conclusion

Statement

Example

Understand the problem

Figure it out!

Try it yourself