10 Coding Interview Mistakes That Cost You the Job

The Mistakes That Kill Your Chances

After analyzing hundreds of failed interviews, these are the patterns that consistently lead to rejection.

Mistake #1: Diving Into Code Immediately

**What happens**: You start coding the moment you hear the problem.

**Why it fails**: Interviewers want to see your thought process. They're evaluating if you can work through ambiguity.

**Fix**: Spend 3-5 minutes clarifying requirements, discussing approach, and getting buy-in before writing code.

Mistake #2: Not Clarifying Edge Cases

**What happens**: You assume inputs are always valid.

**Why it fails**: Edge cases show attention to detail. Missing them suggests you'll write buggy production code.

**Fix**: Always ask about: empty inputs, null values, negative numbers, duplicates, overflow.

Mistake #3: Memorizing Solutions Instead of Patterns

**What happens**: You've seen this exact problem before but can't solve a slight variation.

**Why it fails**: Interviewers often modify classic problems. Pattern recognition beats memorization.

**Fix**: For every problem, ask "What pattern is this?" Two pointers? Sliding window? BFS? DP?

Mistake #4: Silent Coding

**What happens**: You code in silence for 20 minutes.

**Why it fails**: The interviewer has no idea what you're thinking. They can't help if you're going down the wrong path.

**Fix**: Narrate your thoughts. "I'm checking if... Now I'll handle the case where..."

Mistake #5: Ignoring Time Complexity

**What happens**: Your solution works but is O(n^3) when O(n) is possible.

**Why it fails**: At scale, inefficient code causes real problems. FAANG companies care about this.

**Fix**: Before coding, state your approach's time and space complexity. Ask if it's acceptable.

Mistake #6: Not Testing Your Code

**What happens**: You say "done" without running through examples.

**Why it fails**: Small bugs (off-by-one, wrong variable) show carelessness.

**Fix**: Always trace through your code with the given example AND an edge case.

Mistake #7: Getting Defensive About Hints

**What happens**: The interviewer suggests a different approach and you push back.

**Why it fails**: Shows you can't collaborate or accept feedback.

**Fix**: Hints are gifts! "Oh interesting, so you're suggesting I should use a heap here? Let me think about that..."

Mistake #8: Giving Up Too Easily

**What happens**: "I've never seen this problem, I don't know how to do it."

**Why it fails**: Real engineering often involves problems you've never seen.

**Fix**: Break it down. "I'm not sure of the optimal approach, but let me try to solve a simpler version first..."

Mistake #9: Poor Time Management

**What happens**: You spend 40 minutes on approach and have 5 minutes to code.

**Why it fails**: Incomplete solutions rarely pass.

**Fix**: Practice with a timer. 5 min clarify, 10 min approach, 20 min code, 10 min test.

Mistake #10: Not Practicing Under Pressure

**What happens**: You solve problems fine at home but freeze in interviews.

**Why it fails**: Interview anxiety is real. You need exposure to overcome it.

**Fix**: Do mock interviews. Have someone watch you code. Practice explaining your thoughts out loud.

The Solution

Most of these mistakes come from inadequate practice. Not just solving problems, but practicing the full interview experience.

DSA 100 Days includes AI mock interviews that simulate real conditions. [Start practicing today](/signup).