Junior Warmup 10

Hit the floor of every coding-interview rubric: recognize the canonical patterns, narrate trade-offs, and finish a problem in under twenty minutes.

By Alex Chen, Founder, InterviewChamp.AI · 10 problems · ~8h · difficulty: easy · Last verified 2026-05-25

Day 1Two Sum(arrays)
Hash-map intuition. The pattern that opens 30% of array problems.
Day 2Valid Palindrome(strings)
Two pointers from both ends. The pattern that crushes 'check this string' problems.
Day 3Best Time to Buy and Sell Stock(arrays)
Single pass with a running minimum. Train the instinct to ask 'what's the cheapest thing I've seen so far?'
Day 4Valid Anagram(strings)
Counter hash-map. Same template you'll reuse for group-anagrams and ransom-note.
Day 5Reverse Linked List(linked-lists)
Iterative prev/curr/next dance. Memorize this template — fifty other linked-list problems start with it.
Day 6Valid Parentheses(stacks)
Stack as a matching tool. The mental model unlocks daily-temperatures and min-stack later.
Day 7Maximum Depth of Binary Tree(trees)
Recursion on trees: base case = null, recurse = children. Every tree problem starts here.
Day 8Binary Search(binary-search)
Off-by-one is the whole game. Burn the lo/hi/mid template into muscle memory.
Day 9Contains Duplicate(hash-tables)
One-line set check. Use this to practice narrating O(n) time, O(n) space out loud.
Day 10Linked List Cycle(linked-lists)
Floyd's tortoise-and-hare. First non-obvious algorithm in the canon — say the name when you spot the shape.

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