might be making a mistake starting 2018...

2019/day04/part2/main.go

@@ -0,0 +1,80 @@
+/*
+Only change from part1 is adding a decorator to the digit slices to shrink large
+groups (more than 2 digits) into a single digit. Then pass that into the same
+checks for a duplicate & all decreasing
+*/
+
+package main
+
+import "fmt"
+
+func main() {
+	start, end := 138307, 654504
+	possibleCombinations := 0
+
+	for i := start; i <= end; i++ {
+		digits := shrinkLargeGroups(makeDigitsSlice(i))
+		if isIncreasing(digits) && hasDuplicate(digits) {
+			possibleCombinations++
+		}
+	}
+
+	fmt.Println(possibleCombinations)
+}
+
+func makeDigitsSlice(num int) []int {
+	result := make([]int, 6)
+	for i := 5; num > 0; i-- {
+		result[i] = num % 10
+		num -= num % 10
+		num /= 10
+	}
+	return result
+}
+
+/*
+shrinkLargeGroups will return a new slice with any groups larger than 2 shrinked
+down to 1. e.g. 111223 -> 1223
+*/
+func shrinkLargeGroups(digits []int) []int {
+	// from start of number & ensure i+2 is within bounds of the digits slice
+	for i := 0; i+2 < len(digits); i++ {
+		if digits[i] == digits[i+1] && digits[i] == digits[i+2] {
+			// figure out how many items to remove
+			removeUpTo := i + 1
+			for removeUpTo < len(digits) && digits[i] == digits[removeUpTo] {
+				removeUpTo++
+			}
+
+			// copy the values into a new slice
+			newSli := make([]int, 0)
+			for j := 0; j <= i; j++ {
+				newSli = append(newSli, digits[j])
+			}
+			for removeUpTo < len(digits) {
+				newSli = append(newSli, digits[removeUpTo])
+				removeUpTo++
+			}
+			digits = newSli
+		}
+	}
+	return digits
+}
+
+func isIncreasing(digits []int) bool {
+	for i := 1; i < len(digits); i++ {
+		if digits[i] < digits[i-1] {
+			return false
+		}
+	}
+	return true
+}
+
+func hasDuplicate(digits []int) bool {
+	for i := 1; i < len(digits); i++ {
+		if digits[i-1] == digits[i] {
+			return true
+		}
+	}
+	return false
+}