The Trade Desk coding interview
questions, leaked.
5 problems reported across recent The Trade Desk interviews. Top patterns: hash table, string, array. The list below is what most reported candidates actually saw, plus the honest play if you can't grind all of it.
The Trade Desk's interview pulls from a tight dataset. You're looking at five problems across easy to hard, but the pattern is unmistakable: hash-table and string questions dominate. Three of the top problems hinge on hash-table logic, and you'll see strings woven into most of them. The difficulty skews toward medium, which means you won't get a free pass on the easy stuff and you won't face pure algorithmic hellfire either. Most candidates freeze on LRU Cache or Word Ladder because they require holding two concepts at once. StealthCoder handles that wall in seconds if you blank mid-assessment. Know your hash-table tricks cold, because that's where the interview lives.
Top problems at The Trade Desk
| # | Problem | Diff | Frequency | Pass % | Patterns |
|---|---|---|---|---|---|
| 01 | Find the Length of the Longest Common Prefix | MEDIUM | 100.0 | 56% | Array · Hash Table · String |
| 02 | Word Ladder | HARD | 66.1 | 43% | Hash Table · String · Breadth-First Search |
| 03 | LRU Cache | MEDIUM | 66.1 | 45% | Hash Table · Linked List · Design |
| 04 | Best Time to Buy and Sell Stock | EASY | 66.1 | 55% | Array · Dynamic Programming |
| 05 | Basic Calculator II | MEDIUM | 66.1 | 46% | Math · String · Stack |
Frequencies derived from public community-tagged interview reports. Click a row to view on LeetCode.
You have a week, maybe less. You can't out-grind the list above. StealthCoder runs invisibly during the actual The Trade Desk OA. The proctor cannot see it. Screen share cannot detect it. Made by a working Amazon engineer who got tired of watching qualified friends bomb OAs they'd solve cold in an IDE.
Get StealthCoder- hash table3 · 60%
- string3 · 60%
- array2 · 40%
- breadth first search1 · 20%
- linked list1 · 20%
- design1 · 20%
- doubly linked list1 · 20%
- dynamic programming1 · 20%
- trie1 · 20%
- math1 · 20%
Hash tables and strings are your north star here. Three problems sit squarely on hash-table mechanics, and three pull string manipulation into the mix. Array problems appear less often but pop up in the easy and medium tiers, so don't skip Best Time to Buy and Sell Stock just because it looks simple. The hard problem, Word Ladder, combines hash tables with breadth-first search, which catches people off guard because BFS itself is less common in the dataset. LRU Cache is the design curveball that looks like a data-structure problem but tests whether you can actually build something under pressure. Start with hash-table drills, move to string problems, then lock in LRU Cache and Word Ladder. If you hit either of those two during the live assessment and your mind goes blank, StealthCoder runs invisible to the proctor and surfaces a working solution in real time.
Companies with similar patterns
If you prepped for The Trade Desk, these companies recycle ~60% of the same topics.
You've seen the list.
Now make sure you pass The Trade Desk.
Memorizing every problem above in a week is a fantasy. StealthCoder is the hedge: an AI overlay that's invisible during screen share. It reads the problem on screen and surfaces a working solution in under 2 seconds. Made by a working Amazon engineer who got tired of watching qualified friends bomb OAs they'd solve cold in an IDE. Works on HackerRank, CodeSignal, CoderPad, and Karat.
The Trade Desk interview FAQ
Should I spend more time on hash tables or strings?+
Both equally. Three problems use hash tables, three use strings, and LRU Cache ties them together with design. You can't afford to be weak in either. Hash tables first if you're starting from zero, because they're the foundation for Word Ladder and the cache. Strings second, they're the modifier.
Is the easy problem worth studying?+
Yes. Best Time to Buy and Sell Stock looks deceptive. It introduces dynamic-programming thinking in a problem that most people try to brute-force. If you whiff on the easy one, the medium problems hit much harder. Spend an hour on it, understand the state transition, move on.
What's the hardest curveball in The Trade Desk's interview?+
LRU Cache. It's a medium problem that requires you to design a data structure using hash tables and doubly-linked lists simultaneously. Most people know the pieces but can't assemble them under time pressure. Word Ladder is hard but more formulaic once you see the BFS angle.
How many hash-table problems should I drill before the OA?+
At least 10 to 15 beyond the three in this dataset. The Trade Desk's interview is hash-table heavy, so you need pattern recognition, not just memorization. Hit collision resolution, resizing, and then move to problems that use hash tables as a tool inside other algorithms.
Is BFS something I need to worry about?+
Only because it shows up in Word Ladder, which is the hard problem. If you don't know BFS before interview day, you're in trouble. Spend two to three hours on graph traversal, then drill Word Ladder specifically. It's the only BFS problem in the dataset, so it's not a broad pattern here.