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

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

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

Given the intervals below, what is the correct output after merging the overlapping intervals?

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

Given the intervals below, what is the correct output after merging the overlapping intervals?
[ [1, 6], [2, 4] ]

Given the intervals below, what is the correct output after merging the overlapping intervals?

[ [1, 8] ]

Given the intervals below, what is the correct output after merging the overlapping intervals?
[ [1, 8] ]

Given the intervals below, what is the correct output after merging the overlapping intervals?

[ [2, 9], [4, 8], [3, 5] ]

Given the intervals below, what is the correct output after merging the overlapping intervals?
[ [2, 9], [4, 8], [3, 5] ]

Given the intervals below, what is the correct output after merging the overlapping intervals?

[ [3, 5], [2, 4], [4, 5], [6, 10], [12, 14] ]

Given the intervals below, what is the correct output after merging the overlapping intervals?
[ [3, 5], [2, 4], [4, 5], [6, 10], [12, 14] ]

Merge Intervals

Merge Intervals

std::vector<std::vector<int>> MergeIntervals(std::vector<std::vector<int>> &intervals)
{
 // Replace this placeholder return statement with your code
 return {{}};
}

class Interval:
    def __init__(self, start, end):
        self.start = start
        self.end = end
        self.closed = True  # by default, the interval is closed
    # set the flag for closed/open

    def set_closed(self, closed):
        self.closed = closed

    def __str__(self):
        return "[" + str(self.start) + ", " + str(self.end) + "]" \
            if self.closed else \
                "(" + str(self.start) + ", " + str(self.end) + ")"

# 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: `MergeIntervals`\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 `MergeIntervals` 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 `MergeIntervals`.\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) `MergeIntervals`. \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) `MergeIntervals`. \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.

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<int>> val;

 TwoDArray()
 {
 // constructor
 }
 TwoDArray(std::vector<vector<int>> v)
 {
 this->val = 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<int>> 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)
 {
 TwoDArray * custom_ds =(TwoDArray *)input; 
 json result = (json)(custom_ds->val);
 return result.dump();
 // convert 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
 """
 def merge_intervals(intervals):
 intervals.sort(key=lambda x: x[0])
 result = [intervals[0]]
 
 for i in range(1, len(intervals)):
 if intervals[i][0] <= result[-1][1]:
 result[-1][1] = max(result[-1][1], intervals[i][1])
 else:
 result.append([intervals[i][0], intervals[i][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(merge_intervals(self.__inputs[0])))

 if json.dumps(sorted(merge_intervals(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

#include "Solution.cpp"
#include "TwoDArray.cpp"


TwoDArray MergeIntervalsMain(TwoDArray v)
{
 std::vector<std::vector<int>> res = MergeIntervals(v.val);
 TwoDArray convert = *(new TwoDArray(res));
 return convert;
}

private_merge_interval.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : [[4, 6], [3, 7], [1, 5]]
    output: 
    - 1 : [[1, 7]]
  - name: "testcase 2"
    inputs:
    - 1 : [[1, 5], [4, 6], [11, 15], [6, 8]]
    output: 
    - 1 : [[1, 8], [11, 15]]
  
  - name: "testcase 3"
    inputs:
    - 1 : [[1, 5]]
    output: 
    - 1 : [[1, 5]]
  
  - name: "testcase 4"
    inputs:
    - 1 : [[1, 9], [3, 8], [4, 4]]
    output: 
    - 1 : [[1, 9]]
  - name: "testcase 5"
    inputs:
    - 1 : [[1, 2], [8, 8], [3, 4]]
    output: 
    - 1 : [[1, 2], [3, 4], [8, 8]]

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
 """
 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



 # inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 1
 if not is_valid_2d_array(self.__inputs[0]):
 self.store_result ("First argument should be a valid 2D Integer array", ValidationFunction.FAIL)

 elif any(x is None for row in self.__inputs[0] for x in row):
 self.store_result ("First argument should be a valid 2D array", ValidationFunction.FAIL)

 elif not isinstance(self.__inputs[0],list):
 self.store_result ("First argument should be a list", ValidationFunction.FAIL)
 
 elif not all(isinstance(x,list) for x in self.__inputs[0]):
 self.store_result ("Array should contain only lists", ValidationFunction.FAIL)

 elif not all(len(row)==2 for row in self.__inputs[0]):
 self.store_result ("Array should contain only intervals containing two integers", ValidationFunction.FAIL)

 elif not all(isinstance(x,int) and isinstance(y,int) for x,y in self.__inputs[0]):
 self.store_result ("Each interval inside the array should contain only integers", ValidationFunction.FAIL)
 
 elif not (1 <= len(self.__inputs[0]) <= 10**3):
 self.store_result ("length of array should be between 1 and 10^3", ValidationFunction.FAIL)
 
 elif not all([len(x)==2 for x in self.__inputs[0]]):
 self.store_result("length of each interval should be exactly 2", ValidationFunction.FAIL)
 
 elif not all([(0 <= start <= end) for start,end in self.__inputs[0]]):
 self.store_result("Start time should be between 0 and end time, 0 <= start <= end", ValidationFunction.FAIL)

 elif not all([end<=10**4 for start,end in self.__inputs[0]]):
 self.store_result("End time of each interval should be less than or equal to 10^4", ValidationFunction.FAIL) 
 
 else: 
 self.store_result("", ValidationFunction.PASS)

Try to solve the Merge Intervals problem.


Merge Intervals

K-way Merge

Conclusion

Merge Intervals

Statement

Examples

Understand the problem

Figure it out

Try it yourself