From 6068855fa1d0e14c5c6f9f2bf561615e96f44efe Mon Sep 17 00:00:00 2001
From: Brian Buller <brian@bullercodeworks.com>
Date: Wed, 4 Dec 2019 08:40:52 -0600
Subject: [PATCH] 2019 Day 04 Done

---
 2019/day04/main.go |   60 ++
 2019/day04/output  | 1717 ++++++++++++++++++++++++++++++++++++++++++++
 2019/day04/problem |   65 ++
 3 files changed, 1842 insertions(+)
 create mode 100644 2019/day04/main.go
 create mode 100644 2019/day04/output
 create mode 100644 2019/day04/problem

diff --git a/2019/day04/main.go b/2019/day04/main.go
new file mode 100644
index 0000000..df92f86
--- /dev/null
+++ b/2019/day04/main.go
@@ -0,0 +1,60 @@
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+)
+
+func main() {
+	beg, end := []byte("165432"), []byte("707912")
+	if len(os.Args) == 3 {
+		beg, end = []byte(os.Args[1]), []byte(os.Args[2])
+	}
+	var count int
+	for {
+		if validate(beg) {
+			count++
+		}
+		if bytes.Equal(beg, end) {
+			break
+		}
+		beg = inc(beg)
+	}
+	fmt.Println(count)
+}
+
+func inc(num []byte) []byte {
+	if len(num) == 0 {
+		return []byte{'1'}
+	} else if num[len(num)-1] == '9' {
+		return append(inc(num[:len(num)-1]), '0')
+	} else {
+		num[len(num)-1]++
+	}
+	return num
+}
+
+func validate(num []byte) bool {
+	var dup bool
+	for k := range num {
+		if countSeq(num, k) == 2 {
+			dup = true
+		}
+		if len(num) > k+1 && num[k] > num[k+1] {
+			return false
+		}
+	}
+	return dup
+}
+
+func countSeq(num []byte, idx int) int {
+	ret := 1
+	if len(num) > idx+1 && num[idx+1] == num[idx] {
+		ret += countSeq(num[idx+1:], 0)
+	}
+	if idx >= 1 && num[idx-1] == num[idx] {
+		ret += countSeq(num[:idx], idx-1)
+	}
+	return ret
+}
diff --git a/2019/day04/output b/2019/day04/output
new file mode 100644
index 0000000..3703d7a
--- /dev/null
+++ b/2019/day04/output
@@ -0,0 +1,1717 @@
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diff --git a/2019/day04/problem b/2019/day04/problem
new file mode 100644
index 0000000..7ae07ab
--- /dev/null
+++ b/2019/day04/problem
@@ -0,0 +1,65 @@
+Advent of Code
+
+--- Day 4: Secure Container ---
+
+   You arrive at the Venus fuel depot only to discover it's protected by a password. The Elves had written the
+   password on a sticky note, but someone threw it out.
+
+   However, they do remember a few key facts about the password:
+
+     • It is a six-digit number.
+     • The value is within the range given in your puzzle input.
+     • Two adjacent digits are the same (like 22 in 122345).
+     • Going from left to right, the digits never decrease; they only ever increase or stay the same (like 111123 or
+       135679).
+
+   Other than the range rule, the following are true:
+
+     • 111111 meets these criteria (double 11, never decreases).
+     • 223450 does not meet these criteria (decreasing pair of digits 50).
+     • 123789 does not meet these criteria (no double).
+
+   How many different passwords within the range given in your puzzle input meet these criteria?
+
+   Your puzzle answer was 1716.
+
+--- Part Two ---
+
+   An Elf just remembered one more important detail: the two adjacent matching digits are not part of a larger group
+   of matching digits.
+
+   Given this additional criterion, but still ignoring the range rule, the following are now true:
+
+     • 112233 meets these criteria because the digits never decrease and all repeated digits are exactly two digits
+       long.
+     • 123444 no longer meets the criteria (the repeated 44 is part of a larger group of 444).
+     • 111122 meets the criteria (even though 1 is repeated more than twice, it still contains a double 22).
+
+   How many different passwords within the range given in your puzzle input meet all of the criteria?
+
+   Your puzzle answer was 1163.
+
+   Both parts of this puzzle are complete! They provide two gold stars: **
+
+   At this point, you should return to your Advent calendar and try another puzzle.
+
+   Your puzzle input was 165432-707912.
+
+References
+
+   Visible links
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+   . Advent of Code Supporter
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