Valid Arrangement of Pairs
A hard-tier problem at 66% community acceptance, tagged with Depth-First Search, Graph, Eulerian Circuit. Reported in interviews at Snap and 1 others.
Valid Arrangement of Pairs shows up in assessments at Snap and Goldman Sachs, and it catches most candidates off guard because it looks like a simple pairing problem at first. You're given pairs and need to arrange them so each pair's second element matches the next pair's first element. The trick: this is an Eulerian circuit problem disguised as a sorting puzzle. If you don't recognize the pattern, you'll waste 20 minutes building the wrong data structure. StealthCoder spots the graph construction and Hierholzer's algorithm in seconds, invisible to the proctor, so you can submit a working solution even if the pattern didn't click during prep.
Companies that ask "Valid Arrangement of Pairs"
Valid Arrangement of Pairs 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 a senior engineer who knows the OA is theater. This is the script.
Get StealthCoderThe gotcha is that a greedy approach fails. You can't just scan pairs and link them sequentially because you need to use every pair exactly once and form a valid chain. The real solution treats each pair as a directed edge in a graph where the first element is the source and the second is the destination. Then you're finding an Eulerian circuit, a path that visits every edge exactly once. This requires DFS and Hierholzer's algorithm, not basic sorting. Most candidates either miss the graph model entirely or implement DFS wrong on the first try. The conditions for a valid Eulerian circuit are strict: every node must have equal in-degree and out-degree, and the graph must be connected. If you hit this problem live and the structure doesn't feel natural, StealthCoder solves the whole thing, handles edge cases, and gets you past it.
Pattern tags
You know the problem.
Make sure you actually pass it.
Valid Arrangement of Pairs 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 a senior engineer who knows the OA is theater. This is the script. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Valid Arrangement of Pairs interview FAQ
Is Valid Arrangement of Pairs harder than it sounds?+
Yes. It reads like a sorting problem but it's actually a graph problem requiring Eulerian circuit knowledge. The acceptance rate is 66%, meaning a third of candidates who attempt it fail. Most don't recognize the pattern fast enough. That gap is exactly where StealthCoder saves time on the OA.
What's the main trick I'm missing if I think sorting or greedy works?+
You need to model the problem as a directed graph and find an Eulerian circuit using DFS and Hierholzer's algorithm. Greedy fails because you can't guarantee you'll use all pairs or form a valid path. The graph structure is non-obvious but essential.
Do I need to know Eulerian circuits to solve this?+
Practically, yes. If you don't know the pattern, you'll rediscover it under time pressure. Candidates familiar with Eulerian circuits and Hierholzer's algorithm solve it in 15-20 minutes. Others stall. It's a knowledge gate, not a pure algorithm problem.
Is this problem still asked at Snap and Goldman Sachs?+
It's reported from both companies. The data doesn't say how recently, but both Snap and Goldman Sachs are active on harder graph problems. If you're interviewing there, treat this as a real risk for your assessment.
What's the relationship between DFS and Eulerian circuits?+
Hierholzer's algorithm uses DFS or iterative stack-based traversal to build the Eulerian path. You explore edges, backtrack when stuck, and construct the path in reverse. Without understanding that connection, your DFS logic won't work correctly on this problem.
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