116 lines
2.3 KiB
Go
116 lines
2.3 KiB
Go
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package main
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import (
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"os"
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"fmt"
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"strconv"
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"strings"
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)
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// general util
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func check(e error) {
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if e != nil { panic(e) }
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}
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func file_index(mem []int, id int) []int {
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offset := -1
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for i, elem := range mem {
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if elem == id {
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offset = i
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break
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}
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}
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if offset == -1 { return nil }
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length := 1
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for i := offset + 1; i < len(mem); i++ {
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if mem[i] == id {
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length++
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} else {
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break
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}
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}
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return []int{offset, offset + length}
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}
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func cp(mem []int, id int) bool {
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file_idx := file_index(mem, id)
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file_len := file_idx[1] - file_idx[0]
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target_mem := mem[:file_idx[0]]
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i := 0
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for {
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if i > len(target_mem) { break }
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space_idx := file_index(target_mem[i:], -1)
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if space_idx == nil { break }
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space_len := space_idx[1] - space_idx[0]
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if space_len >= file_len {
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// copy
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copy(mem[i + space_idx[0]: i + space_idx[1]], mem[file_idx[0]:file_idx[1]])
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return true
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}
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i += space_idx[1] + 1
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}
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return false
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}
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// main loop
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func main() {
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// read in file
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dat, err := os.ReadFile("data.txt")
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check(err)
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dat_str := strings.TrimSpace(string(dat))
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// contruct input as int arr
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input := make([]int, 0, len(dat_str))
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mem_size := 0
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for _, char := range []rune(dat_str) {
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num, err := strconv.Atoi(string(char))
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check(err)
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mem_size += num
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input = append(input, num)
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}
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// convert to actual memory representation
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mem := make([]int, 0, mem_size)
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is_file := true
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file_id := 0
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for _, elem := range input {
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if is_file {
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for range elem {
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mem = append(mem, file_id)
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}
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file_id++
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} else {
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for range elem {
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mem = append(mem, -1)
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}
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}
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is_file = !is_file
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}
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// reorder
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for i := file_id - 1; i > 0; i-- {
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file_idx := file_index(mem, i)
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if cp(mem, i) {
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// clear old file
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for i := file_idx[0]; i < file_idx[1]; i++ { mem[i] = -1 }
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}
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}
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// calc checksum
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checksum := 0
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for i, elem := range mem {
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if elem == -1 { continue }
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checksum += i * elem
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}
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fmt.Println(checksum)
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}
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