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path: root/go/run-length-encoding/run_length_encoding.go
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package encode

import (
	"fmt"
	"strings"
)

func encodeLength(s string) (n int) {
	var last rune
	for _, c := range s {
		if last == 0 {
			last = c
		}
		if c != last {
			break
		}
		n++
	}
	return n
}

func RunLengthEncode(input string) string {
	var s strings.Builder
	for len(input) != 0 {
		n := encodeLength(input)
		if n == 1 {
			fmt.Fprintf(&s, "%c", input[0])
		} else {
			fmt.Fprintf(&s, "%d%c", n, input[0])
		}
		input = input[n:]
	}
	return s.String()
}

func decodeLength(s string) (number, count int) {
	for _, c := range s {
		if c >= '0' && c <= '9' {
			number *= 10
			number += int(c) - '0'
			count++
		} else {
			break
		}
	}
	if number == 0 {
		number = 1
	}
	return number, count
}

func RunLengthDecode(input string) string {
	var s strings.Builder
	for len(input) > 0 {
		n, c := decodeLength(input)
		s.WriteString(strings.Repeat(string(input[c]), n))
		input = input[c+1:]
	}
	return s.String()
}