# Bitap Algorithm

This is a exact 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 m = pattern.Length;
int R;
int i;

if (string.IsNullOrEmpty(pattern)) return 0;
if (m > 31) return -1; //Error: The pattern is too long!

R = ~1;

for (i = 0; i <= 127; ++i)

for (i = 0; i < m; ++i)

for (i = 0; i < text.Length; ++i)
{
R <<= 1;

if (0 == (R & (1 << m)))
return (i - m) + 1;
}

return -1;
}```
```

### Example

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

### Output

```									`index: 16`
```