AoC 2020: day4

Signed-off-by: Ettore Dreucci <ettore.dreucci@gmail.com>

2019-go/day_04/day_04.go

@@ -0,0 +1,67 @@
+package main
+
+import "fmt"
+
+const (
+	min = 130254
+	max = 678275
+)
+
+func intToSlice(n int) []int {
+	s := make([]int, 0)
+	for n != 0 {
+		r := n % 10
+		n = n / 10
+		s = append([]int{r}, s...)
+	}
+	return s
+}
+
+func twoEqualAdjacentDigits(pwd []int) bool {
+	l := len(pwd)
+	for i := 0; i < l-1; i++ {
+		if pwd[i] == pwd[i+1] {
+			return true
+		}
+	}
+	return false
+}
+
+func twoExclusiveAdjacentDigits(pwd []int) bool {
+	l := len(pwd)
+	for i := 0; i < l-1; i++ {
+		if pwd[i] == pwd[i+1] && (i == 0 || pwd[i] != pwd[i-1]) && (i == l-2 || pwd[i] != pwd[i+2]) {
+			return true
+		}
+	}
+	return false
+}
+
+func increasingDigits(pwd []int) bool {
+	for i, digit := range pwd {
+		if i < len(pwd)-1 && digit > pwd[i+1] {
+			return false
+		}
+	}
+	return true
+}
+
+func main() {
+	// Part 1:
+	count1, count2 := 0, 0
+	for i := min; i < max; i++ {
+		pwd := intToSlice(i)
+		two := twoEqualAdjacentDigits(pwd)
+		onlyTwo := twoExclusiveAdjacentDigits(pwd)
+		if increasingDigits(pwd) {
+			if two {
+				count1++
+			}
+			if onlyTwo {
+				count2++
+			}
+		}
+	}
+	fmt.Printf("Part 1: %d\n", count1)
+	fmt.Printf("Part 2: %d\n", count2)
+}