problem 79 in goHEADmaster

1 files changed, 98 insertions, 0 deletions

diff --git a/go/079-passcode_derivation.go b/go/079-passcode_derivation.go
new file mode 100644
index 0000000..001d2f8
--- /dev/null
+++ b/go/079-passcode_derivation.go
@@ -0,0 +1,98 @@
+/*
+* 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
+	}
+
+}