Longest Path With Different Adjacent Characters
A hard-tier problem at 54% community acceptance, tagged with Array, String, Tree. Reported in interviews at Target and 2 others.
Longest Path With Different Adjacent Characters is a hard problem that's been asked at Target, Hudson River Trading, and Uber. At 53% acceptance, it's rough: the naive greedy approach fails, and most candidates initially miss that this is actually a graph traversal problem hiding in plain sight. You're given a string or tree where adjacent characters must differ, and you need to find the longest valid path. The trick isn't obvious on first read, which is exactly when StealthCoder matters. If you hit this live and your initial solution times out or gives a wrong answer, you have an invisible safety net that surfaces a working approach in seconds.
Companies that ask "Longest Path With Different Adjacent Characters"
Longest Path With Different Adjacent Characters is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share.
Get StealthCoderThe core trap is thinking this is a simple DP or greedy problem. It's not. This is a graph traversal problem that often requires DFS or topological sort to avoid revisiting nodes and to correctly handle the constraint that adjacent characters must be different. Many candidates code a recursive backtracking solution that's correct but inefficient, or they miss that the graph structure matters more than the string itself. The problem tests whether you can identify the right algorithmic pattern (DFS/topological sort) rather than just character comparison. Common pitfalls include forgetting to track visited nodes, incorrectly handling the adjacency constraint in recursive calls, and not recognizing when memoization helps. StealthCoder's value here is immediate: when your first approach fails on test cases or TLE hits, you don't have time to rethink the entire strategy during the assessment. A working solution appears instantly.
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Longest Path With Different Adjacent Characters recycles across companies for a reason. It's hard-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Longest Path With Different Adjacent Characters interview FAQ
Is this really a tree problem or a graph problem?+
The topics list includes both Tree and Graph. The structure often looks like a tree, but the adjacency constraint (different adjacent characters) and the need to find the longest path require graph traversal thinking. Treat the input as a directed or undirected graph and use DFS or topological sort accordingly.
Why does greedy fail here?+
Greedy (always pick the next valid character) doesn't guarantee the longest path because backtracking is needed. You may skip a character early that would unlock a longer path later. DFS with memoization forces you to explore all valid branches and compare results correctly.
Is this still asked at big tech companies?+
Yes. Target, Hudson River Trading, and Uber have all asked it. At 53% acceptance, it's a clear filtering problem. If it shows up in your online assessment, you're being tested on graph pattern recognition under time pressure.
What's the role of topological sort?+
If the problem encodes dependencies or a DAG structure (where character transitions matter), topological sort helps process nodes in a valid order and compute longest paths efficiently. It's one of two main approaches, alongside DFS with memoization.
How much time should I spend on this before moving on?+
In a real assessment, if your initial solution doesn't pass small test cases within 10-15 minutes, you've likely chosen the wrong pattern. At that point, switching your mental model to graph traversal is critical. StealthCoder is the hedge for that exact moment.
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