How Can We Efficiently Find All Overlapping Pattern Matches in a Go String?

Overlapping Pattern Matching in Go

In Go, the use of regular expressions to match overlapping patterns can be challenging. The FindAllStringSubmatchIndex method, while useful for non-overlapping matches, falls short when dealing with patterns that overlap.

An Alternative Approach

Instead of solely relying on regular expressions, we can employ a simpler and more efficient solution using the strings.Index function and a for loop. This approach offers a straightforward way to identify all occurrences of an overlapping pattern, regardless of its position within the input string.

Code Example

The following code snippet demonstrates this alternative approach:

import (
    "fmt"
    "strings"
)

func main() {
    input := "...#...#....#.....#..#..#..#......."
    idx := []int{}
    j := 0
    for {
        i := strings.Index(input[j:], "..#..")
        if i == -1 {
            break
        }
        idx = append(idx, j+i)
        j += i + 1
    }
    fmt.Println("Indexes:", idx)
}

In this code, the Index function is used to search for the pattern "..#.." within the input string starting from position 'j'. When a match is found, the index of the matching position is added to the idx slice, and 'j' is incremented by 'i 1' to move the search to the next character after the match.

Results

When executed, the code prints the following output:

1
10
16
22
Indexes: [1 10 16 22]

This output correctly identifies all overlapping occurrences of the "..#.." pattern in the input string.

Conclusion

While regular expressions can be a powerful tool for pattern matching in many scenarios, they may not be the most suitable option for cases involving overlapping patterns. By leveraging the simplicity and efficiency of string operations, we can effectively solve such problems without the complexities of regular expression parsing.

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