1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
|
/*
* Passcode derivation
* Problem 79
*
* A common security method used for online banking is to ask the user for three random
* characters from a passcode. For example, if the passcode was 531278, they may ask for the
* 2nd, 3rd, and 5th characters; the expected reply would be: 317.
* The text file, keylog.txt, contains fifty successful login attempts.
* Given that the three characters are always asked for in order, analyse the file so as to
* determine the shortest possible secret passcode of unknown length.
*/
package main
import "fmt"
var PASSCODE_PARTS = [...][3]int{
{3, 1, 9},
{6, 8, 0},
{1, 8, 0},
{6, 9, 0},
{1, 2, 9},
{6, 2, 0},
{7, 6, 2},
{6, 8, 9},
{7, 6, 2},
{3, 1, 8},
{3, 6, 8},
{7, 1, 0},
{7, 2, 0},
{7, 1, 0},
{6, 2, 9},
{1, 6, 8},
{1, 6, 0},
{6, 8, 9},
{7, 1, 6},
{7, 3, 1},
{7, 3, 6},
{7, 2, 9},
{3, 1, 6},
{7, 2, 9},
{7, 2, 9},
{7, 1, 0},
{7, 6, 9},
{2, 9, 0},
{7, 1, 9},
{6, 8, 0},
{3, 1, 8},
{3, 8, 9},
{1, 6, 2},
{2, 8, 9},
{1, 6, 2},
{7, 1, 8},
{7, 2, 9},
{3, 1, 9},
{7, 9, 0},
{6, 8, 0},
{8, 9, 0},
{3, 6, 2},
{3, 1, 9},
{7, 6, 0},
{3, 1, 6},
{7, 2, 9},
{3, 8, 0},
{3, 1, 9},
{7, 2, 8},
{7, 1, 6},
}
// dumb brute force approch (takes about 1min to solve)
func main() {
mainLoop:
for passcode := 100; ; passcode++ {
s := fmt.Sprintf("%d", passcode)
digits := make([]int, 0, len(s))
for _, c := range s {
digits = append(digits, int(c - '0'))
}
for _, part := range PASSCODE_PARTS {
validCount := 0
for _, d := range digits {
if d == part[validCount] {
validCount++
}
if validCount == 3 {
break
}
}
if validCount != 3 {
continue mainLoop
}
}
fmt.Println(passcode)
break
}
}
|
