package main
import (
	"bufio"
	"log"
	"os"
	"sort"
	"strconv"
)
type JointDiff [3]int
func main() {
	if err := realMain(); err != nil {
		log.Println(err)
	}
}
func realMain() error {
	joltOut, err := parseInput("input.txt")
	if err != nil {
		return err
	}
	joltOut = addDeviceJolt(joltOut)
	joltOut = append(joltOut, 0)
	sort.Ints(joltOut)
	diffs := solveFirst(joltOut)
	log.Println("Part1:", diffs[0]*diffs[2])
	return nil
}
func solveFirst(jolts []int) JointDiff {
	sum := JointDiff{}
	for i, jt := range jolts {
		if i == 0 {
			continue
		}
		switch jt - jolts[i-1] {
		case 1:
			sum[0]++
		case 2:
			sum[1]++
		case 3:
			sum[2]++
		default:
			log.Panicln("invalid diff")
		}
	}
	return sum
}
func addDeviceJolt(jolts []int) []int {
	var max int
	for _, j := range jolts {
		if j > max {
			max = j
		}
	}
	return append(jolts, max+3)
}
func parseInput(fileName string) ([]int, error) {
	fd, err := os.Open(fileName)
	if err != nil {
		return nil, err
	}
	defer fd.Close()
	var ret []int
	buf := bufio.NewScanner(fd)
	for buf.Scan() {
		tmp, err := strconv.Atoi(buf.Text())
		if err != nil {
			return nil, err
		}
		ret = append(ret, tmp)
	}
	return ret, nil
}

66
7
73
162
62
165
157
158
137
125
138
59
36
40
94
95
13
35
136
96
156
155
24
84
42
171
142
3
104
149
83
129
19
122
68
103
74
118
20
110
54
127
88
31
135
26
126
2
51
91
16
65
128
119
67
48
111
29
49
12
132
17
41
166
75
146
50
30
1
164
112
34
18
72
97
145
11
117
58
78
152
90
172
163
89
107
45
37
79
159
141
105
10
115
69
170
25
100
80
4
85
169
106
57
116
23

28
33
18
42
31
14
46
20
48
47
24
23
49
45
19
38
39
11
1
32
25
35
8
17
7
9
4
2
34
10
3

module main
go 1.17