horspool.go

package horspool

// User defined.
// Set to true to read input from two command line arguments
// Set to false to read input from two files "pattern.txt" and "text.txt"
// const commandLineInput bool = false

// Implementation of Boyer-Moore-Horspool algorithm (Suffix based approach).
// Requires either a two command line arguments separated by a single space,
// or two files in the same folder: "pattern.txt" containing the string to
// be searched for, "text.txt" containing the text to be searched in.
// func main() {
// 	if commandLineInput == true { // case of command line input
// 		args := os.Args
// 		if len(args) <= 2 {
// 			log.Fatal("Not enough arguments. Two string arguments separated by spaces are required!")
// 		}
// 		pattern := args[1]
// 		s := args[2]
// 		for i := 3; i < len(args); i++ {
// 			s = s + " " + args[i]
// 		}
// 		if len(args[1]) > len(s) {
// 			log.Fatal("Pattern  is longer than text!")
// 		}
// 		fmt.Printf("\nRunning: Horspool algorithm.\n\n")
// 		fmt.Printf("Search word (%d chars long): %q.\n", len(args[1]), pattern)
// 		fmt.Printf("Text        (%d chars long): %q.\n\n", len(s), s)
// 		horspool(s, pattern)
// 	} else if commandLineInput == false { // case of file line input
// 		patFile, err := ioutil.ReadFile("pattern.txt")
// 		if err != nil {
// 			log.Fatal(err)
// 		}
// 		textFile, err := ioutil.ReadFile("text.txt")
// 		if err != nil {
// 			log.Fatal(err)
// 		}
// 		if len(patFile) > len(textFile) {
// 			log.Fatal("Pattern  is longer than text!")
// 		}
// 		fmt.Printf("\nRunning: Horspool algorithm.\n\n")
// 		fmt.Printf("Search word (%d chars long): %q.\n", len(patFile), patFile)
// 		fmt.Printf("Text        (%d chars long): %q.\n\n", len(textFile), textFile)
// 		horspool(string(textFile), string(patFile))
// 	}
// }

// // Function horspool performing the Horspool algorithm.
// // Prints whether the word/pattern was found and on what position in the text or not.
// func horspool(t, p string) {
// 	m, n, c, pos := len(p), len(t), 0, 0
// 	//Perprocessing
// 	d := preprocess(t, p)
// 	//Map output
// 	fmt.Printf("Precomputed shifts per symbol: ")
// 	for key, value := range d {
// 		fmt.Printf("%c:%d; ", key, value)
// 	}
// 	fmt.Println()
// 	//Searching
// 	for pos <= n-m {
// 		j := m
// 		if t[pos+j-1] != p[j-1] {
// 			fmt.Printf("\n   comparing characters %c %c at positions %d %d", t[pos+j-1], p[j-1], pos+j-1, j-1)
// 			c++
// 		}
// 		for j > 0 && t[pos+j-1] == p[j-1] {
// 			fmt.Printf("\n   comparing characters %c %c at positions %d %d", t[pos+j-1], p[j-1], pos+j-1, j-1)
// 			c++
// 			fmt.Printf(" - match")
// 			j--
// 		}
// 		if j == 0 {
// 			fmt.Printf("\n\nWord %q was found at position %d in %q. \n%d comparisons were done.", p, pos, t, c)
// 			return
// 		}
// 		pos = pos + d[t[pos+m]]
// 	}
// 	fmt.Printf("\n\nWord was not found.\n%d comparisons were done.", c)
// 	return
// }

// // Function that pre-computes map with Key: uint8 (char) Value: int.
// // Values determine safe shifting of search window.
// func preprocess(t, p string) (d map[uint8]int) {
// 	d = make(map[uint8]int)
// 	for i := 0; i < len(t); i++ {
// 		d[t[i]] = len(p)
// 	}
// 	for i := 0; i < len(p); i++ {
// 		d[p[i]] = len(p) - i
// 	}
// 	return d
// }