# Fuzzy Bitap Algorithm

This is a fuzzy string matching version of bitap algorithm. The bitap algorithm (also known as the **shift-or**, **shift-and** or **Baeza-Yates–Gonnet** algorithm) is an approximate string matching algorithm. The algorithm tells whether a given text contains a substring which is "approximately equal" to a given pattern, where approximate equality is defined in terms of Levenshtein distance — if the substring and pattern are within a given distance k of each other, then the algorithm considers them equal. The algorithm begins by precomputing a set of bitmasks containing one bit for each element of the pattern. Then it is able to do most of the work with bitwise operations, which are extremely fast.

` ````
public static int SearchString(string text, string pattern, int k)
{
int result = -1;
int m = pattern.Length;
int[] R;
int[] patternMask = new int[128];
int i, d;
if (string.IsNullOrEmpty(pattern)) return 0;
if (m > 31) return -1; //Error: The pattern is too long!
R = new int[(k + 1) * sizeof(int)];
for (i = 0; i <= k; ++i)
R[i] = ~1;
for (i = 0; i <= 127; ++i)
patternMask[i] = ~0;
for (i = 0; i < m; ++i)
patternMask[pattern[i]] &= ~(1 << i);
for (i = 0; i < text.Length; ++i)
{
int oldRd1 = R[0];
R[0] |= patternMask[text[i]];
R[0] <<= 1;
for (d = 1; d <= k; ++d)
{
int tmp = R[d];
R[d] = (oldRd1 & (R[d] | patternMask[text[i]])) << 1;
oldRd1 = tmp;
}
if (0 == (R[k] & (1 << m)))
{
result = (i - m) + 1;
break;
}
}
return result;
}
```

### Example

` ``int index = SearchString("The quick brown foax jumps over the lazy dog", "fox", 1);`

### Output

` ``index: 16`