Learn and practice the Merge Intervals and K-way Merge patterns to solve coding interview problems.

Educative-77 in Java: Accelerate Your Coding Interview Prep

Many information processing and decision-support problems require us to merge information coming from multiple sources to build up a global picture of a situation before making some business decisions. This module will help us understand and deploy two common coding patterns used to merge lists of structurally homogeneous data to solve hard problems that we encounter, for example, in scheduling, social media applications, and I/O algorithms.

Fusion

# Statement

You’re given a list containing the schedules of multiple employees. Each person’s schedule is a list of non-overlapping intervals in sorted order. An interval is specified with the start and end time, both being positive integers. Your task is to find the list of finite intervals representing the free time for all the employees.

> **Note:** The common free intervals are calculated between the earliest start time and the latest end time of all meetings across all employees.

**Constraints:**

* $1 \leq$ `schedule.length` , `schedule[i].length` $\leq 50$

* $0 \leq$ `interval.start` < `interval.end` $\leq 10^8$, where `interval` is any interval in the list of schedules.

# Examples


# 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:

From the given list of employee schedules, find the list of intervals representing the free time for all the employees.

[[[3, 5], [8, 10]], [[4, 6], [9, 12]], [[5, 6], [8, 10]]]

From the given list of employee schedules, find the list of intervals representing the free time for all the employees.
[[[3, 5], [8, 10]], [[4, 6], [9, 12]], [[5, 6], [8, 10]]]

From the given list of employee schedules, find the list of intervals representing the free time for all the employees.

[[[1, 3], [5, 6], [9, 10]],[[2, 4], [7, 8]], [[8, 11], [12, 14]]]

From the given list of employee schedules, find the list of intervals representing the free time for all the employees.
[[[1, 3], [5, 6], [9, 10]],[[2, 4], [7, 8]], [[8, 11], [12, 14]]]

From the given list of employee schedules, find the list of intervals representing the free time for all the employees.

[[[1, 2], [3, 4]], [[2, 3]], [[4, 6]]]

From the given list of employee schedules, find the list of intervals representing the free time for all the employees.
[[[1, 2], [3, 4]], [[2, 3]], [[4, 6]]]

Employee Free Time

Employee Free Time


# 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 `EmployeeFreeTimes.java` in the following coding playground. We have provided the definition of the `Interval` class in the other file. You may add functionality to this class if you wish.





import java.util.*;
class Interval{
    int start;
    int end;
    boolean closed;
    public Interval(int start, int end)
    {
        this.start = start;
        this.end = end;
        this.closed = true; // by default, the interval is closed
    }
        
    // set the flag for closed/open
    public void setClosed(boolean closed)
    {
        this.closed = closed;
    }
 
}

import java.util.*;

class Solution {
 public static List<Interval> employeeFreeTime(List<List<Interval>> schedule) {

 // Replace this placeholder return statement with your code

 List<Interval> ans = new ArrayList<Interval>();
 return ans;
 }
}

Help me debug only the function Employee Free Time . . 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 employeeFreeTime function and the other function(s) invoked in it/them. Do not review extra/helper files or functions not invoked in the solution function employeeFreeTime. 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 Merge Intervals pattern used? Take your time and review the code.

Please provide a brief time complexity analysis of the function employeeFreeTime. While calculating time complexity, include the time complexity of built-in Java 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 employeeFreeTime. While calculating space complexity, include the space complexity of built-in Java 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

ThreeDArray

TwoDArray

import ds_v1.DataStructure.DataStructure;
import java.util.*;
import com.fasterxml.jackson.databind.*;

import ds_v1.DataStructure.DataStructure;

import java.io.IOException;
import java.util.List;
import com.fasterxml.jackson.core.type.TypeReference;

public class ThreeDArray extends DataStructure {

 // define class attributes
 public List<List<List<Integer>>> value;
 //public List<List<Integer>> value1;
 private void generateError(String data) {
 System.err.println("ThreeDArray is not parsable: " + data);
 System.exit(-1);
 }
 public ThreeDArray() {
 // constructor
 }
 
 public ThreeDArray(List<List<List<Integer>>> data) {
 // constructor 
 this.value = new ArrayList<List<List<Integer>>>();
 for(int i = 0; i < data.size(); i++)
 {
 this.value.add(new ArrayList<List<Integer>>());
 for(int j = 0; j < data.get(i).size(); j++)
 {
 this.value.get(i).add(new ArrayList<>());
 this.value.get(i).get(j).add(data.get(i).get(j).get(0));
 this.value.get(i).get(j).add(data.get(i).get(j).get(1));
 }
 }

 }
 

 public String toString() {
 // override toString() for your data structure
 return "";
 }


 private List<List<List<Integer>>> construct_int_arr(String new_value) {
 List<List<List<Integer>>> arr = null;
 try {
 arr = new ObjectMapper().readValue(new_value, new TypeReference<List<List<List<Integer>>>>() {
 });
 } catch (IOException e) {
 }
 return arr;
 }

 // return value will be passed to user program
 @Override
 public ThreeDArray construct(String new_value3, Integer type_of_ds) {
 // parse test case in json string 'value' to your desired data structure
 List<List<List<Integer>>> value = construct_int_arr(new_value3);
 return new ThreeDArray(value); 
 }

 // 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();
 }

}

import ds_v1.DataStructure.DataStructure;

import java.util.*;
import com.fasterxml.jackson.databind.*;

import ds_v1.DataStructure.DataStructure;

import java.io.IOException;
import java.util.List;
import com.fasterxml.jackson.core.type.TypeReference;
public class TwoDArray extends DataStructure {

 // define class attributes
 public List<List<Integer>> value;
 private void generateError(String data) {
 System.err.println("TwoDArray is not parsable: " + data);
 System.exit(-1);
 }

 public TwoDArray() {
 // constructor
 }
 public TwoDArray(List<List<Integer>> data) {
 // constructor
 // constructor
 value = new ArrayList<List<Integer>>();
 for(int i = 0; i < data.size(); i++)
 {
 value.add(new ArrayList<Integer>());
 for(int j = 0; j < data.get(i).size(); j++)
 {
 value.get(i).add(data.get(i).get(j));
 }
 }
 }

 public String toString() {
 // override toString() for your data structure
 return this.value.toString();
 }

 // 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
 return new TwoDArray();

 }

 // 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 TwoDArray
 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
 """
 def employee_free_time(schedule):
 import heapq
 heap = []

 for i in range(len(schedule)):
 heap.append((schedule[i][0][0], i, 0))

 heapq.heapify(heap)

 result = []
 previous = schedule[heap[0][1]][heap[0][2]][0]

 while heap:
 _, i, j = heapq.heappop(heap)
 interval = schedule[i][j]

 if interval[0] > previous:
 result.append([previous, interval[0]])

 previous = max(previous, interval[1])

 if j + 1 < len(schedule[i]):
 heapq.heappush(heap, (schedule[i][j + 1][0], i, j + 1))

 return result





 # 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(sorted(employee_free_time(self.__inputs[0])))

 if json.dumps(sorted(employee_free_time(self.__inputs[0]))) == json.dumps(sorted(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.*;
//import java.awt.List;
public class Main{
 public static TwoDArray sum (ThreeDArray input_1) {
 List<List<Interval>> list = new ArrayList<List<Interval>>();
 List<List<Integer>> data = new ArrayList<List<Integer>>();
 for(int i = 0; i < input_1.value.size(); i++)
 {
 list.add(new ArrayList<Interval>());
 for(int j = 0; j < input_1.value.get(i).size(); j++)
 {
 list.get(i).add(new Interval(input_1.value.get(i).get(j).get(0), input_1.value.get(i).get(j).get(1)));
 }
 }
 List<Interval> lList1 = Solution.employeeFreeTime(list);
 for(int i = 0; i < lList1.size(); i++)
 {
 data.add(new ArrayList<>());
 data.get(i).add(lList1.get(i).start);
 data.get(i).add(lList1.get(i).end);
 }
 return new TwoDArray(data);
 }
}

employee_free_time.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : [[[1, 2], [5, 6]], [[1, 3]], [[4, 10]]]
    output: 
    - 1 : [[3,4]]
  - name: "testcase 2"
    inputs:
    - 1 : [[[1, 3], [6, 7]], [[2, 4]], [[2, 5], [9, 12]]]
    output: 
    - 1 : [[5,6],[7,9]]
  - name: "testcase 3"
    inputs:
    - 1 : [[[2, 3], [7, 9]], [[1, 4], [6, 7]]]
    output: 
    - 1 : [[4,6]]
  - name: "testcase 4"
    inputs:
    - 1 : [[[3, 5], [8, 10]], [[4, 6], [9, 12]], [[5, 6], [8, 10]]]
    output: 
    - 1 : [[6,8]]
  - name: "testcase 5"
    inputs:
    - 1 : [[[1, 2], [3, 4], [5, 6], [7, 8], [9, 10], [11, 12]], [[1, 2], [3, 4], [5, 6], [7, 8], [9, 10], [11, 12]], [[1, 2], [3, 4], [5, 6], [7, 8], [9, 10], [11, 12]], [[1, 2], [3, 4], [5, 6], [7, 8], [9, 10], [11, 12]]]
    output: 
    - 1 : [[2, 3], [4, 5], [6, 7], [8, 9], [10, 11]]

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
 """
 # inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 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, int) for elem in row):
 return False 
 return True

 
 
 if not isinstance(self.__inputs[0],list):
 self.store_result ("Invalid input type", ValidationFunction.FAIL)



 elif not all(is_valid_2d_array(schedule) for schedule in self.__inputs[0]):
 self.store_result ("Invalid input type", ValidationFunction.FAIL)

 
 
 elif not isinstance(self.__inputs[0],list):
 self.store_result ("The input should be a list", ValidationFunction.FAIL)
 
 elif not all(isinstance(x,list) for x in self.__inputs[0]):
 self.store_result ("The input array should contain only lists", ValidationFunction.FAIL)

 
 elif not all([len(x)==2 for schedule in self.__inputs[0] for x in schedule]):

 self.store_result("Length of each interval should be exactly 2", ValidationFunction.FAIL)
 
 
 elif not all(isinstance(x,int) and isinstance(y,int) for i in self.__inputs[0] for x,y in i):
 self.store_result ("Each interval inside an employee's schedule should contain only integers", ValidationFunction.FAIL)

 
 
 
 elif not (1 <= len(self.__inputs[0]) <= 50):
 self.store_result ("Length of input should be between 1 and 50", ValidationFunction.FAIL)

 elif not all( (1 <= len(x) <= 50 ) for x in self.__inputs[0]):
 self.store_result ("Length of each employee's schedule should be between 1 and 50", ValidationFunction.FAIL)
 

 
 elif not all(0 <= start < end for i in self.__inputs[0] for start,end in i):
 self.store_result ("Start time in each interval should be greater than or equal to 0 and less than its end time", ValidationFunction.FAIL)

 
 elif not all(end<=10**8 for i in self.__inputs[0] for start,end in i):
 self.store_result ("End time in each interval should be less than or equal to 10^8", ValidationFunction.FAIL)

 
 
 

 

 elif not all([x[y+1][0]>=x[y][1] for x in self.__inputs[0] for y in range(len(x)-1)]):
 self.store_result ("Intervals in each schedule should be non-overlapping", ValidationFunction.FAIL)

 


 else:
 self.store_result("", ValidationFunction.PASS)

Try to solve the Employee Free Time problem.

Merge Intervals

K-way Merge

Conclusion

Employee Free Time

Statement

Examples

Understand the problem

Figure it out!

Try it yourself