Coding problem: Fewest Edits Between Strings. Return the minimum number of single-character edits that turn the string `a` into the string `b`. One edit inserts a character, deletes a character, or replaces one character with another.

What the interviewer is looking for

• What a strong solution looks like: DP table d[i][j] = edits to turn a[:i] into b[:j]; d[i][0] = i, d[0][j] = j; d[i][j] = d[i-1][j-1] if a[i-1] == b[j-1], else 1 + min(d[i-1][j], d[i][j-1], d[i-1][j-1]). O(|a|·|b|) time; O(min(|a|, |b|)) space keeping two rows.
• Think aloud. Interviewers are judging how you reason, not only the final code.
• Be ready for: Reconstruct the actual edits. Only need to know whether the distance is <= k — can you do O(n·k) (banded DP)? Suggest spelling corrections from a dictionary of a million words quickly (BK-tree, tries, n-gram filters). Allow swapping adjacent characters as one edit.

A structure to follow: Clarify, plan, code, test, analyse

1. Step 1

   Clarify

   Restate the problem, ask about empty input, duplicates and size limits, and agree on one example.

2. Step 2

   Plan

   Say the simple approach first and its cost, then the better one. Explain why before you type.

3. Step 3

   Code

   Write small named steps and talk through each. A clear solution beats a clever one.

4. Step 4

   Test

   Walk your own example through the code, then an edge case. Fix what you find calmly.

5. Step 5

   Analyse

   State time and space cost in plain words and say what you would change for much larger input.

This is guidance on shape, not a script. Use your own real experience and facts; never invent details to fill a gap. See the STAR guide and answer frameworks.

Common slips

• Starting to code before agreeing what the answer must be.
• Going silent when stuck instead of saying what you are trying.
• Never running your own example through the code.

How to practise it

Solve it once in the editor without hints, then explain your solution aloud in under two minutes.

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