day 1

01/main.go

@@ -0,0 +1,93 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+// Given a list of paired integers with columns representing two groups,
+// compute the total distance between pairs in the sorted lists.
+func main() {
+
+	// open input file
+
+	input, err := os.ReadFile("input")
+	if err != nil {
+		fmt.Println(err)
+	}
+
+	// Walk the list and create two lists, left and right
+	left, right := extractLists(string(input))
+
+	// Sort left and right
+	sort.Slice(left, func(i, j int) bool {
+		return left[i] < left[j]
+	})
+	sort.Slice(right, func(i, j int) bool {
+		return right[i] < right[j]
+	})
+
+	// lFreqMap := frequencyMap(left)
+	rFreqMap := frequencyMap(right)
+
+	// Walk through left and compare each element to its pair in right
+
+	differenceTotal := 0
+	scoreTotal := 0
+	for idx, val := range left {
+		var l, r int
+		l = val
+		r = right[idx]
+
+		// Sum distance between elements
+		difference := l - r
+		score := l * rFreqMap[l]
+
+		// Take absolute value
+		if difference < 0 {
+			difference = -difference
+		}
+		differenceTotal += difference
+		scoreTotal += score
+	}
+
+	// Return total distance
+
+	fmt.Println(differenceTotal)
+	fmt.Println(scoreTotal)
+}
+
+func frequencyMap(slice []int) map[int]int {
+	frequency := make(map[int]int) // val -> score
+
+	for _, val := range slice {
+		frequency[val] = frequency[val] + 1
+	}
+
+	return frequency
+}
+
+func extractLists(input string) ([]int, []int) {
+	var left, right []int
+	for _, val := range strings.Split(input, "\n") {
+		// fmt.Println(idx)
+		t := strings.Fields(val)
+		if len(t) < 2 {
+			continue
+		}
+		l, err := strconv.Atoi(t[0])
+		if err != nil {
+			panic("aaa")
+		}
+		left = append(left, l)
+		r, err := strconv.Atoi(t[1])
+		if err != nil {
+			panic("bbb")
+		}
+		right = append(right, r)
+	}
+	return left, right
+}