Write a function that, given an x, y coordinate of a land cell, returns all water cells that touch that island.
The key idea is to traverse the entire island starting from the given land cell, then collect every adjacent water cell that touches any boundary of that island. A DFS or BFS works well: first visit all connected land cells, and for each cell check its four neighbors. If a neighbor is water, add it to the result set to avoid duplicates. This is a standard grid-connected-component search problem, typically solved with traversal plus a visited set.
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