# Faster distance editing algorithm

**Problem:** I know the trivial formulation of DP distance and computation in O (mn) for 2 rows of size n and m respectively. But recently I found out that if we only need to calculate the minimum value of the edit distance f and it is limited to | f | <= s, then we can compute it in O (min (m, n) + s ^ 2) or O (s * min (m, n)) [wikipedia] time.

Please explain the dp wording behind it if it is based on DP or explain the algorithm.

Take a look at the `improved algorithm`

link section : http://en.wikipedia.org/wiki/Edit_distance .

another link about improved UKKONEN algorithm http://www.berghel.net/publications/asm/asm.php

Thanks in advance.

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You can calculate edit distance in O (min (n, m) * s) using the following simple idea:

Consider the i-th row in the DP table.

So, if we know that the answer is <= s, then we interstit in cells with coordinates (i, i - s), (i, i - s + 1), ..., (i, i + s). Because in other cells the answer is strictly more than s.

For example, suppose we know that the edit distance between "abacaba" and "baadba" is less than 3.

So, we can skip the red cells because they have a value greater than s.

The asymptotics of the algorithm is O (min (n, m) * s), since we compute s-cells to the left and right of the main diagonal.

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