# Edit Distance and Edit Steps

One of the interesting things about

`NSMetadataQuery`

is that after it has done its initial “gathering” of the results, all further updates are reported as a single array of results. Did something get added to the results? Here’s a new array of the state of all results now. Did something get removed? Here’s another array.[…]

In other words, the Levenshtein algorithm can

easilybe generalized to work on any`CollectionType`

of`Equatables`

. Suddenly, it looks like just the thing we need to implement more-efficient array diffing.One downside of the Levenshtein algorithm is that it only returns an

`Int`

. It only tells us how many steps we would need, but not what the actual stepsare. For that, we’ll turn to a specific implementation of the Levenshtein algorithm, called the Wagner-Fischer algorithm.

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