day4. day5 is weird.

day4/main.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+func numMatching(sliceToEnd []rune) int {
+	// fmt.Println(sliceToEnd)
+	// gets in a slice from a character to the end, returns an int of the matching characters
+	result := 1
+	for i := 1; i < len(sliceToEnd); i++ {
+		if sliceToEnd[i] == sliceToEnd[0] {
+			result += 1
+		} else {
+			break
+		}
+	}
+	// fmt.Println(result)
+	return result
+}
+
+func testNumber(num int) bool {
+	// cast to string to iterate through digits?
+	strNum := strconv.Itoa(num)
+	runesSlice := []rune(strNum)
+
+	duplicate := false
+
+	for i := 0; i < len(runesSlice)-1; {
+		if runesSlice[i] > runesSlice[i+1] {
+			return false
+		}
+
+		matches := numMatching(runesSlice[i:len(runesSlice)])
+		if matches == 2 {
+			duplicate = true
+			i++
+		} else if matches == 1 {
+			i++
+		} else if matches > 2 {
+			i += (matches - 1)
+		}
+	}
+
+	// if the entire for loop passes, return if there was a duplicate or not
+	return duplicate
+}
+
+func main() {
+	start, end := 138307, 654504
+	possibleCombinations := 0
+
+	for i := start; i <= end; i++ {
+		if testNumber(i) {
+			possibleCombinations++
+		}
+	}
+
+	fmt.Println(possibleCombinations)
+	// fmt.Println(testNumber(111122))
+	// fmt.Println(testNumber(123444))
+	// fmt.Println(testNumber(112233))
+}