Island Perimeter
A easy-tier problem at 74% community acceptance, tagged with Array, Depth-First Search, Breadth-First Search. Reported in interviews at Cadence and 1 others.
Island Perimeter is an easy matrix problem that appears deceptively simple but trips up candidates who overthink it. You're given a 2D grid where 1 represents land and 0 represents water, and you need to calculate the perimeter of the island. Cadence and Oracle both ask this. The 70% acceptance rate masks a common pitfall: candidates write complex DFS or BFS traversals when a direct counting approach is faster and cleaner. If you hit this in your OA and freeze on the traversal overhead, StealthCoder solves it in seconds while the proctor sees nothing.
Companies that ask "Island Perimeter"
Island Perimeter 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 trick isn't graph traversal at all. Each land cell contributes 4 units of perimeter by default. Subtract 2 for each shared edge with another land cell (since that edge is internal, not perimeter). You can iterate through the grid once, and for each land cell, check its right and bottom neighbors. Every land-to-land adjacency you find reduces the total by 2. This runs in O(n*m) time with O(1) space and avoids the overhead of DFS or BFS stack management entirely. Candidates often default to traversal patterns because they see 'matrix' and 'connected cells' and assume it's a graph problem. It's not. The perimeter calculation is arithmetic. When you're live and second-guessing whether you need DFS, StealthCoder will confirm the counting method works and show the code in seconds.
Pattern tags
You know the problem.
Make sure you actually pass it.
Island Perimeter recycles across companies for a reason. It's easy-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.
Island Perimeter interview FAQ
Do I actually need DFS or BFS for Island Perimeter?+
No. This is a counting problem disguised as a graph problem. Iterate the grid once, count land cells and their shared edges. DFS/BFS adds unnecessary complexity and time overhead. The simple approach is faster and what interviewers expect.
Is Island Perimeter still asked at Cadence and Oracle?+
Yes, both companies have reportedly asked it. At easy difficulty with a 70% pass rate, it's a screening problem meant to filter for algorithmic thinking, not to stump you. If you know the counting trick, you'll pass.
What's the most common mistake on this problem?+
Implementing DFS or BFS to visit every land cell and count perimeter edges, then getting bogged down in visited tracking and recursion. The direct count method (4 units per cell minus 2 per shared edge) is shorter, faster, and less error-prone.
How does Island Perimeter relate to Array and Matrix topics?+
It's a 2D array problem that tests your ability to iterate a matrix and check neighbors. It doesn't require graph algorithms despite the layout. Understanding neighbor relationships in a grid is the core skill.
Can I solve Island Perimeter without checking neighbors?+
No, you need to detect which edges are shared with other land cells to subtract them. But you only need to check two directions (right and bottom) per cell to avoid double-counting, keeping the logic clean.
Want the actual problem statement? View "Island Perimeter" on LeetCode →