Free AI LeetCode Communication Coach — Merge Intervals

The problem

Given intervals[i] = [start, end], merge all overlapping intervals.

Example: intervals = [[1,3],[2,6],[8,10],[15,18]] → [[1,6],[8,10],[15,18]]

Sort first — say it.

intervals.sort()
merged = [intervals[0]]
for start, end in intervals[1:]:
    if start <= merged[-1][1]:
        merged[-1][1] = max(merged[-1][1], end)
    else:
        merged.append([start, end])
return merged

How to explain it

1. 1. Restate

   Say the problem in your own words.

   One or two sentences. Show you understood the input, the output, and the goal — not that you memorised the prompt.

2. 2. Approach

   Name the method before you code.

   Brute force first if you need it, then the structure you will use: hash map, two pointers, stack, binary search.

3. 3. Example

   Walk one concrete input.

   Pick small numbers. Say what you store, what you compare, and what you return. Interviewers follow an example more easily than abstract talk.

4. 4. Time and space

   One sentence each.

   After the example, before you claim you are done. “Time is O(n) because we scan once. Space is O(n) for the map.”

5. 5. Edge cases

   Name at least one unusual input.

   Empty input, duplicates, already sorted, overflow. Invite a follow-up: “I would also check …”

• “I sort by start.”
• “If it overlaps I extend the end; else I push a new interval.”

Practise out loud

1. 1. Restate

   I need to merge overlapping intervals into a non-overlapping list.

2. 2. Approach

   I sort by start time. I scan once: if the next interval overlaps the current end, I extend the end; otherwise I push a new interval.

3. 3. Example

   On [1,3] and [2,6], 2 is not after 3, so I merge to [1,6]. [8,10] does not overlap, so I start a new one.

4. 4. Time and space

   Time is O(n log n) from the sort. Space is O(n) for the output.

5. 5. Edge cases

   I would check an empty list and a case where one interval fully contains another.

Common mistakes when explaining Merge Intervals

• Forgetting to sort first.
• Saying O(n) when sorting dominates.