Merge pull request #385 from vaskoz/day186

Day186

README.md

@@ -195,3 +195,4 @@ problems from
 * [Day 182](https://github.com/vaskoz/dailycodingproblem-go/issues/376)
 * [Day 184](https://github.com/vaskoz/dailycodingproblem-go/issues/378)
 * [Day 185](https://github.com/vaskoz/dailycodingproblem-go/issues/381)
+* [Day 186](https://github.com/vaskoz/dailycodingproblem-go/issues/382)

day186/problem.go

@@ -0,0 +1,47 @@
+package day186
+
+// SubsetsSmallestDifference returns the two subsets with the
+// smallest difference between them.
+// Brute-force. Runs in O(2^N) time.
+func SubsetsSmallestDifference(nums []int) ([]int, []int) {
+	perms := make(chan [][]int)
+	go func() {
+		permutations(nums, []int{}, []int{}, perms)
+		close(perms)
+	}()
+	minSum := int(^uint(0) >> 1)
+	var s1, s2 []int
+	for subsets := range perms {
+		if s := sum(subsets[0], subsets[1]); s < minSum {
+			minSum = s
+			s1 = subsets[0]
+			s2 = subsets[1]
+		}
+	}
+	return s1, s2
+}
+
+func sum(s1, s2 []int) int {
+	sum := 0
+	for _, v := range s1 {
+		sum += v
+	}
+	for _, v := range s2 {
+		sum -= v
+	}
+	if sum < 0 {
+		return -sum
+	}
+	return sum
+}
+
+func permutations(nums, sub1, sub2 []int, perms chan [][]int) {
+	if len(nums) == 0 {
+		newS1 := append([]int{}, sub1...)
+		newS2 := append([]int{}, sub2...)
+		perms <- [][]int{newS1, newS2}
+		return
+	}
+	permutations(nums[1:], append(sub1, nums[0]), sub2, perms)
+	permutations(nums[1:], sub1, append(sub2, nums[0]), perms)
+}

day186/problem_test.go

@@ -0,0 +1,29 @@
+package day186
+
+import (
+	"testing"
+)
+
+var testcases = []struct {
+	nums []int
+	diff int
+}{
+	{[]int{5, 10, 15, 20, 25}, 5},
+}
+
+func TestSubsetsSmallestDifference(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if s1, s2 := SubsetsSmallestDifference(tc.nums); sum(s1, s2) != tc.diff {
+			t.Errorf("Expected a diff of %v, got (%v,%v) for a diff of %v", tc.diff, s1, s2, sum(s1, s2))
+		}
+	}
+}
+
+func BenchmarkSubsetsSmallestDifference(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			SubsetsSmallestDifference(tc.nums)
+		}
+	}
+}