Writing Clean Interview Code

Clean code in interviews isn't about perfection -- it's about demonstrating that you write professional, readable code even under pressure.

Language Choice

Language	Pros for Interviews	Cons
Python	Concise, readable, fast to write, built-in data structures	Slower runtime (rarely matters in interviews)
Java	Strong typing, explicit, popular in Big Tech	Verbose, more boilerplate
JavaScript	Universal, good for frontend roles	No built-in heap, unusual in some companies
C++	Fast, shows systems knowledge	Most verbose, easy syntax errors

Recommendation: Use Python unless the role specifically requires another language. It lets you write the most code in the least time.

Code Organization Rules

1. Meaningful Variable Names

# Bad
def f(a, t):
    d = {}
    for i, v in enumerate(a):
        c = t - v
        if c in d:
            return [d[c], i]
        d[v] = i

# Good
def two_sum(nums, target):
    seen = {}
    for index, num in enumerate(nums):
        complement = target - num
        if complement in seen:
            return [seen[complement], index]
        seen[num] = index

2. Helper Functions

Break complex logic into named functions:

# Without helpers (hard to follow)
def solve(board):
    for i in range(9):
        for j in range(9):
            if board[i][j] == '.':
                for c in '123456789':
                    if all(board[i][k] != c for k in range(9)) and \
                       all(board[k][j] != c for k in range(9)) and \
                       all(board[3*(i//3)+di][3*(j//3)+dj] != c
                           for di in range(3) for dj in range(3)):
                        board[i][j] = c
                        if solve(board): return True
                        board[i][j] = '.'
                return False
    return True

# With helpers (clear intent)
def solve(board):
    def is_valid(row, col, num):
        # Check row
        if num in board[row]: return False
        # Check column
        if any(board[r][col] == num for r in range(9)): return False
        # Check 3x3 box
        box_r, box_c = 3 * (row // 3), 3 * (col // 3)
        for r in range(box_r, box_r + 3):
            for c in range(box_c, box_c + 3):
                if board[r][c] == num: return False
        return True

    def backtrack():
        for r in range(9):
            for c in range(9):
                if board[r][c] == '.':
                    for num in '123456789':
                        if is_valid(r, c, num):
                            board[r][c] = num
                            if backtrack(): return True
                            board[r][c] = '.'
                    return False
        return True

    return backtrack()

3. Early Returns

Reduce nesting with early returns:

# Deeply nested (hard to read)
def process(node):
    if node:
        if node.val > 0:
            if node.left:
                return process(node.left)
            else:
                return node.val
        else:
            return 0
    else:
        return -1

# Early returns (much cleaner)
def process(node):
    if not node:
        return -1
    if node.val <= 0:
        return 0
    if not node.left:
        return node.val
    return process(node.left)

Common Pitfalls

Pitfall	Fix
Off-by-one errors	Use range(n) for 0 to n-1; range(1, n+1) for 1 to n
Integer overflow	Python handles big integers; in Java/C++ use long
Null/None checks	Check before accessing .val, .next, .left
Modifying list while iterating	Iterate over a copy or use index-based loop
Forgetting to handle empty input	Add guard clause at the top

Testing Your Code

After coding, trace through your solution:

# Your solution
def max_profit(prices):
    min_price = float('inf')
    max_profit = 0
    for price in prices:
        min_price = min(min_price, price)
        max_profit = max(max_profit, price - min_price)
    return max_profit

# Trace: prices = [7, 1, 5, 3, 6, 4]
# price=7: min=7, profit=0
# price=1: min=1, profit=0
# price=5: min=1, profit=4
# price=3: min=1, profit=4
# price=6: min=1, profit=5 ✓
# price=4: min=1, profit=5
# Result: 5 ✓

Interview Tip: After finishing your code, say: "Let me trace through this with our example to verify." This shows thoroughness and catches bugs before the interviewer does.

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Next, let's cover the new AI-era skills that companies are testing in 2026. :::