Why Intervals Are a Common Problem Pattern in DSA Python - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to merge overlapping intervals.

DSA Python

intervals.sort(key=lambda x: x[[1]])

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A0

B-1

C2

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Sorting by the end time instead of start time.

Using an invalid index like 2 or -1.

We sort intervals by their start time, which is at index 0.

2fill in blank

medium

Complete the code to check if current interval overlaps with the last merged interval.

DSA Python

if intervals[i][[1]] <= merged[-1][1]:

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A1

B-1

C2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing the end time of current interval instead of start time.

Using wrong index for start time.

We compare the start of the current interval (index 0) with the end of the last merged interval.

3fill in blank

hard

Fix the error in updating the end time of the last merged interval.

DSA Python

merged[-1][1] = max(merged[-1][1], intervals[i][[1]])

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A1

B0

C2

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using start time index instead of end time.

Using negative index incorrectly.

The end time is at index 1, so we take the max of last merged end and current interval end.

4fill in blank

hard

Fill both blanks to create a list of merged intervals.

DSA Python

merged = [intervals[[1]]]
for i in range(1, [2]):
    # merging logic here

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A0

Blen(intervals)

C1

Dintervals

Attempts:

3 left

💡 Hint

Common Mistakes

Starting merged list with wrong index.

Looping with incorrect range.

Start merged list with first interval at index 0, then loop from 1 to length of intervals.

5fill in blank

hard

Fill all three blanks to complete the dictionary comprehension that counts interval overlaps by start time.

DSA Python

overlap_count = { [1]: sum(1 for interval in intervals if interval[[2]] == start) for start in [3] }

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Astart

B0

C[interval[0] for interval in intervals]

Dinterval

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names in comprehension.

Using wrong index for start time.

We create a dictionary with keys as start times, counting how many intervals start at each time.