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path: root/go/ocr-numbers/ocr_numbers.go
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package ocr

import (
	"bufio"
	"bytes"
	"fmt"
	"strings"
)

/*
 _     _  _     _  _  _  _  _
| |  | _| _||_||_ |_   ||_||_|
|_|  ||_  _|  | _||_|  ||_| _|

*/

var rules = []map[string][]int{
	{ // 1. line
		" _ ": []int{0, 2, 3, 5, 6, 7, 8, 9},
		"   ": []int{1, 4},
	},
	{ // 2. line
		"| |": []int{0},
		"  |": []int{1, 7},
		" _|": []int{2, 3},
		"|_ ": []int{5, 6},
		"|_|": []int{4, 8, 9},
	},
	{ // 3. line
		"|_|": []int{0, 6, 8},
		"  |": []int{1, 4, 7},
		"|_ ": []int{2},
		" _|": []int{3, 5, 9},
	},
	{ // 4. line
		"   ": []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
	},
}

func splitByDigit(line string) []string {
	ret := make([]string, len(line)/3)
	for i := range ret {
		ret[i] = line[i*3 : i*3+3]
	}
	return ret
}

func toString(r [][]int) string {
	buf := new(bytes.Buffer)
	for _, v := range r {
		if len(v) == 1 {
			fmt.Fprint(buf, v[0])
		} else {
			fmt.Fprint(buf, "?")
		}
	}
	return buf.String()
}

func intersection(a, b []int) []int {
	isInSet := func(x []int, a int) bool {
		for _, v := range x {
			if v == a {
				return true
			}
		}
		return false
	}
	var r []int
	for _, v := range a {
		if isInSet(b, v) {
			r = append(r, v)
		}
	}
	return r
}

func recognizeDigit(s []string, set [][]int, k int) [][]int {
	if set == nil {
		set = make([][]int, len(s))
		for i := range set {
			set[i] = []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
		}
	}
	ret := make([][]int, len(s))
	for i, v := range s {
		if r, ok := rules[k][v]; ok {
			ret[i] = intersection(set[i], r)
		}
	}
	return ret
}

func Recognize(s string) []string {
	scan := bufio.NewScanner(strings.NewReader(s))
	var set [][]int
	var ret []string
	for i := 0; scan.Scan(); {
		if t := scan.Text(); len(t) > 0 {
			dig := splitByDigit(t)
			set = recognizeDigit(dig, set, i)
			if i++; i == 4 {
				str := toString(set)
				ret = append(ret, str)
				set = nil
				i = 0
			}
		}
	}
	return ret
}