Merge 10d8dba into c4c7dfb

README.md

@@ -436,6 +436,7 @@ problems from
 * [Day 437](https://github.com/vaskoz/dailycodingproblem-go/issues/875)
 * [Day 438](https://github.com/vaskoz/dailycodingproblem-go/issues/873)
 * [Day 439](https://github.com/vaskoz/dailycodingproblem-go/issues/886)
+* [Day 441](https://github.com/vaskoz/dailycodingproblem-go/issues/896)
 * [Day 442](https://github.com/vaskoz/dailycodingproblem-go/issues/894)
 * [Day 443](https://github.com/vaskoz/dailycodingproblem-go/issues/892)
 * [Day 444](https://github.com/vaskoz/dailycodingproblem-go/issues/890)

day441/problem.go

@@ -0,0 +1,33 @@
+package day441
+
+import "sort"
+
+// DNFPartitionBrute has values smaller than pivot first, followed by pivot values,
+// followed by values larger than pivot last.
+// Runs in O(N log N) because it just sorts.
+func DNFPartitionBrute(lst []int, pivot int) {
+	sort.Ints(lst)
+}
+
+// DNFPartition has values smaller than pivot first, followed by pivot values,
+// followed by values larger than pivot last.
+// Runs in O(N) because it just sorts.
+func DNFPartition(lst []int, pivot int) {
+	var i, j int
+
+	n := len(lst) - 1
+
+	for j <= n {
+		switch {
+		case lst[j] < pivot:
+			lst[i], lst[j] = lst[j], lst[i]
+			i++
+			j++
+		case lst[j] > pivot:
+			lst[j], lst[n] = lst[n], lst[j]
+			n--
+		default:
+			j++
+		}
+	}
+}

day441/problem_test.go

@@ -0,0 +1,74 @@
+package day441
+
+import "testing"
+
+// nolint
+var testcases = []struct {
+	lst   []int
+	pivot int
+}{
+	{[]int{9, 12, 3, 5, 14, 10, 10}, 10},
+	{[]int{9, 12, 3, 5, 14, 10, 10}, 20},
+	{[]int{9, 12, 3, 5, 14, 10, 10}, 1},
+}
+
+func checkInvariant(lst []int, pivot int) bool {
+	var i int
+	for i < len(lst) && lst[i] < pivot {
+		i++
+	}
+
+	for i < len(lst) && lst[i] == pivot {
+		i++
+	}
+
+	for i < len(lst) && lst[i] > pivot {
+		i++
+	}
+
+	return i == len(lst)
+}
+
+func TestDNFPartitionBrute(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range testcases {
+		copied := append([]int{}, tc.lst...)
+		DNFPartitionBrute(copied, tc.pivot)
+
+		if !checkInvariant(copied, tc.pivot) {
+			t.Errorf("Didn't partition correctly. pivot=%d. Given %v got %v", tc.pivot, tc.lst, copied)
+		}
+	}
+}
+
+func BenchmarkDNFPartitionBrute(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			copied := append([]int{}, tc.lst...)
+			DNFPartitionBrute(copied, tc.pivot)
+		}
+	}
+}
+
+func TestDNFPartition(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range testcases {
+		copied := append([]int{}, tc.lst...)
+		DNFPartition(copied, tc.pivot)
+
+		if !checkInvariant(copied, tc.pivot) {
+			t.Errorf("Didn't partition correctly. pivot=%d. Given %v got %v", tc.pivot, tc.lst, copied)
+		}
+	}
+}
+
+func BenchmarkDNFPartition(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			copied := append([]int{}, tc.lst...)
+			DNFPartition(copied, tc.pivot)
+		}
+	}
+}