day 464: cleaned up day 198

day464/problem.go

@@ -0,0 +1,52 @@
+package day464
+
+import (
+	"sort"
+)
+
+// LargestSubsetPairs finds the largest subset
+// such that every pair of elements in the subset (i, j)
+// satisfies either i % j = 0 or j % i = 0.
+// Runs in O(N^2) time
+func LargestSubsetPairs(nums []int) []int {
+	sort.Slice(nums, func(i, j int) bool {
+		return nums[i] < nums[j]
+	})
+
+	dp := make([]int, len(nums))
+	dp[len(dp)-1] = 1
+	largestI, largestVal := 0, 0
+
+	for i := len(dp) - 2; i >= 0; i-- {
+		m := 0
+
+		for j := i + 1; j < len(dp); j++ {
+			if nums[j]%nums[i] == 0 {
+				m = max(m, dp[j])
+			}
+		}
+
+		if dp[i] = 1 + m; dp[i] > largestVal {
+			largestI = i
+			largestVal = dp[i]
+		}
+	}
+
+	result := make([]int, 0, largestVal)
+
+	for i := largestI; i < len(nums); i++ {
+		if nums[i]%nums[largestI] == 0 {
+			result = append(result, nums[i])
+		}
+	}
+
+	return result
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+
+	return b
+}

day464/problem_test.go

@@ -0,0 +1,34 @@
+package day464
+
+import (
+	"reflect"
+	"testing"
+)
+
+// nolint
+var testcases = []struct {
+	nums, subset []int
+}{
+	{[]int{3, 5, 10, 20, 21}, []int{5, 10, 20}},
+	{[]int{1, 3, 6, 24}, []int{1, 3, 6, 24}},
+}
+
+func TestLargestSubsetPairs(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range testcases {
+		input := append([]int{}, tc.nums...)
+		if result := LargestSubsetPairs(input); !reflect.DeepEqual(result, tc.subset) {
+			t.Errorf("Expected %v, got %v", tc.subset, result)
+		}
+	}
+}
+
+func BenchmarkLargestSubsetPairs(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			input := append([]int{}, tc.nums...)
+			LargestSubsetPairs(input)
+		}
+	}
+}