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Asked: 2026-05-25T11:46:29+00:00

I have a 2-dimensional integer array (say 1000 by 1000), let’s call it matrix.

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I have a 2-dimensional integer array (say 1000 by 1000), let’s call it matrix. Each cell in this matrix has a X- and Y-coordinate (each from 0 to 999 in this example). Initially all grid cells have a value of 0. During program runtime, some of the matrix cells are set to another value <> 0.

Now I need a fast function (algorithm) that takes some X and Y values and returns the value of the matrix at that coordinates. However, if the matrix at the specified X/Y location is 0, then the algorithm should determine a non-zero value within the matrix that is as close to the original X/Y location as possible.

I have thought about looping around the original X/Y position with increasing offset at each loop cycle, but I am not sure whether this is really the fastest algorithm…

Any ideas? I would prefer Java code, but any pseudo-code is also fine 🙂

Thanks in advance for your help!
Kind regards, Matthias

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1 Answer

  1. Editorial Team

    If the array is relatively sparse and the number of tests is high relative to the number of inserts, the naive approach could take a long time.

    The alternative is to build a spatial-partition tree such as a quadtree or k-d tree. Nearest-neighbor search is O(ln N) at the cost of O(ln N) insert times.

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