- Snowflake – What It Is and Why It Exists
Start here. What Snowflake actually is — a SQL data warehouse you rent by the second, on somebody else's cloud — and what problem it was built to solve that Postgres and Hadoop did not. What you get on day one, what you pay for, when it is the wrong tool, and the lesson index for this track in reading order.
- LeetCode 7 – Reverse Integer
Tagged Easy, and it is not quite. Reversing the digits takes four lines; the problem is detecting 32-bit overflow without being allowed a 64-bit type. Two ways to check — undo the step, or rearrange the inequality — plus why Java's truncating % carries the sign for free, why Math.abs breaks on Integer.MIN_VALUE, and why Python needs the opposite care because its integers never overflow.
- LeetCode 5 – Longest Palindromic Substring
Counting substrings is O(n³) and the DP table costs O(n²) memory. Neither is the answer you want: a string has only 2n − 1 centres, and expanding around each one is O(n²) time in O(1) space and about fifteen lines. The even-length centre everyone forgets, the hi − lo − 1 off-by-one, the interval DP for when you need it, and where Manacher's linear algorithm fits.
- LeetCode 2 – Add Two Numbers
Long addition wearing a linked list costume. Reverse digit order is a gift, not an obstacle — it points the lists the same way the carry travels. The dummy head that removes the first-node special case, the carry in the loop condition that gives 999 + 1 its fourth node, and why converting to an integer overflows on the real test cases. Java and Python, plus the forward-order follow-up.
- LeetCode 1 – Two Sum
The first problem on LeetCode, and still the most common phone-screen warm-up. It is not a test of whether you can find two numbers — it is a test of whether you reach for a hash map the moment you catch yourself writing a nested loop. One pass, look up before you insert, and the target = 2 × nums[i] case that lets an element pair with itself. Java and Python, plus the sorted two-pointer variant that 3Sum is built on.